Guren Ichinose

Guren Ichinose 「一瀬グレン, Ichinose Guren」 is the main protagonist of the Owari no Seraph: Ichinose Guren, Jyuurokusai no Catastrophe series and an important character in the Owari no Seraph series. He is a Lieutenant Colonel of the Japanese Imperial Demon Army and the commanding officer of the Vampire Extermination Unit's Moon Demon Company.

Appearance
Guren is a tall, young man with medium length black hair parted in the middle and purple eyes. He sometimes wear his hair slicked back.

He wears the standard JIDA uniform which consists of a long-sleeved black coat with red details including the shoulder epaulettes, an aiguillette worn on the right shoulder with a five-pointed star decoration, and two rows of gold buttons on the front. Along with that, he wears a pair of white gloves, an armband on his left arm, and a white web belt with a gold waist-plate. He also wears the uniform trousers with two white belts around his left leg and black shoes.

Personality
Guren was naive in his childhood days and spent most of his time with Mahiru. His aspects on life felt simple as he was in his happy moments. But after he was treated with disgust due to his name as a lowly born branch member, he began to feel guilt. He thought that because of his weak physique and power, he couldn't reach out for what he wanted, which was hinted to be Mahiru. She motivated him to become stronger and wiser.

He is a wise leader who values teamwork and cooperation, determined to preserve the survival of the human race from demons and vampires. When Yu wanted to join the Moon Demon Company, Guren refuses to allow him until he made friends.

He pretends to be lazy, but he actually works hard and keeps many secrets, which he has no difficulty lying about. He plans to dethrone the Hīragi Family.

He cares about his subordinates and friends, considering them to be family.

History
Guren was born into the Ichinose family, a low branch family of the Hīragi. He was also the best friend and lover of Mahiru Hīragi, but this was frowned upon because of his low birth. Since they were friends, Guren was treated badly and blamed for, also getting beaten by the adults.

He appeared at the end of chapter 1, using information from a prophecy to collect Yūichirō Hyakuya, a survivor of the Hyakuya orphanage. Guren has led Yūichirō to join the Japanese Imperial Demon Army after the moment he has escaped the city of vampire. He is secretly attempting something to reform the Imperial Demon Army governed by the Hīragi Family.

Story: Light Novel
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Prologue
Guren arrived outside the entrance of Sanguinem during the daytime at the end of chapter 1. He says that one of the lab rats from the Hyakuya laboratories, the company responsible for destroying Japan, is there just like the prophecy said. He tells Yu that he will be useful in exterminating vampires. Exactly what prophecy he refers to has yet to be mentioned again in the series.

Second Shibuya High School Arc
Over the next four years, Guren trains Yu to become a soldier of the Japanese Imperial Army. He teaches him how to survive above ground, how to live in the Demon Army's cities, and how to use a sword. Unfortunately, he is less successful at teaching Yu obedience and subordination, which is shown in 2020 in Shibuya, Tokyo at the beginning of chapter 2. Once Yu is sentenced to high school for his disobedience, Guren assigns Shinoa Hīragi to act as Yu's surveillance officer. When Yu refuses to follow orders to make friends, Shinoa gives him a note with the written orders. This note is the first time anyone in the series addresses Yu as a "virgin." Although Shinoa mocks him for being a virgin most often, Guren may have given her the idea to do so in the first place.

During those four years, he also worked on human experimentation for the development of Black Demon Series bearers.

Shinoa finds Guren during chapter 2, alerting him that a vampire escaped onto the school grounds. Guren kills the vampire attacking Yu, giving her an unpleasant surprise when she realizes he used a cursed blade.

Again Guren rejects Yu's request to join the Moon Demon Company to exterminate vampires. Yoichi appears, tackling Yu and appearing as his friend. Guren makes good on his promise, finally accepting Yu to the Moon Demon Company along with Yoichi.

Shinoa informs Guren when Yu manages to overcome a myo-o demon's thrall on his own. After that, Yu and Yoichi attend their first class class in the Moon Demon Company barracks. After he introduces them, Yu picks a fight with Guren, and Guren assigns Yu the seat in front of Kimizuki. Naturally, the two boys start another fight, and Guren finishes it.

Later on, Kimizuki arrives in Guren's office and asks him if he can receive a demon weapon since he is stronger than Yu, but Guren turns him down, warning him that he will be devoured by the demon if he has no bonds to pull him free from the demon's clutches. At the end of chapter 4, Shinoa recommends both Yu and Kimizuki to Guren as candidates for the Black Demon Series weaponry. He plans to rebel against the main family.

In the following chapter, we see him rebelling by sleeping and snoring during a meeting with the higher-ups. He manages to escape a "stupid" political meeting by appearing rude. Yu attacks him, and he decides to proceed with Yu's training so that the upper brass do not notice him. He kicks Yu in the head before continuing with his day.

In chapter 6, Guren appears in the classroom. Sayuri informs him that Yoichi may be stable enough to resist demonic temptation. Guren attacks the classroom, filling with a demonic aura that sends most of the class tumbling to the floor, many of whom go unconscious. Sayuri struggles to stand by using two spell tags. Yu and Kimizuki tremble. Shinoa manages to remain standing just fine, and Yoichi is completely unaffected by the attack to the point where he does not even feel it. They are the only ones standing. Since he experimented on the three boys previously for this purpose, he is not surprised when they stay standing. Contrary to his expectations, Shinoa remains standing as well, proving herself as a possible candidate for Black Demon Series Cursed Gear as well, much to Guren's chagrin.

Before he takes the three boys to make contracts with demons, Sayuri informs Guren that Yoichi may not be strong enough to accept the demon, although his heart is very stable. Guren takes him anyway.

Yoichi becomes possessed, and Guren orders Yu and Kimizuki to kill him. In the end, they manage to help Yoichi regain control and turn back to normal from being a man-eating demon, and it is actually Guren's words that make him snap out of it. Shinoa wonders if Guren planned this ending from the start.

Shinjuku Arc
When Guren assigns Mitsuba Sangū as the fifth member of Shinoa's squad, she protests against being assigned to a squad of rookies, especially working under Shinoa. Eventually, she submits.

Guren and his team enter the field early on in the battle at Shinjuku. He scouts for the enemy commander, spying Mika and Ferid. Ferid spies him back, which Guren finds mildly concerning. Then, he charges in at the 5th Street intersection, killing several vampires with a single strike. He leads the battle, facing off against Mika.

At the Shinjuku 5th Street intersection, Guren and Mika fight head-to-head. Although Guren complements Mika's strength, Mika responds by saying Guren is not very strong. Guren uses a fudo myo-o spell to cause on explosion. Mika dodges easily, but Ferid warns Mika his arrogance will be his downfall and offers his assistance once more. He points out that Guren never planned to fight Mika one-on-one. Shigure set a trap, but Mika manages to escape. With the help of Goshi's illusion, Guren attacks Mika from behind, claiming checkmate. However, Ferid steps between them and blocks the attack. He backhands Guren and sends him flying. Mika lets Guren talk for a few seconds with his team, and Guren decides to take a second potentially lethal pill. However, Mika attacks him before Guren can ingest the medication. When Guren asks if Mika has gotten faster than before, Mika claims he stopped holding back. Guren calls him a naive brat. Mika defeats Guren and stabs him through the chest.

When he attempts to kill Mika with Yu's help, Yu freezes, and Mika escapes. Enraged over Guren, Yu arrives. Mika recognizes him and turns around, but Yu pierces Mika through the chest with Asuramaru, calling him a bloodsucker and telling him to die. Then, he recognizes his not-quite-dead best friend and family member. Guren grasps Mika's sword with a spell tag and urges Yu to activate his weapon and kill the vampire, but Yu freezes when he realizes who he just stabbed. Mika releases his sword and escapes. Guren hits Yu and asks him why he did not kill that vampire when he had the chance,

Although Yu desperately wants to reclaim Mika, Guren issues orders to retreat. Ferid plays with Guren, eventually grabbing him by the neck. Ferid swindles his opportunity to kill Guren, and he asks him about Yu, even though Ferid already knows the answers. Guren calls Yu's transformation his "ace in the hole" after subduing the it by commanding Shinoa to embrace Yu. Guren makes a comment about being a decoy, and Ferid notices Shinya, barely escaping a sniping attack. The main forces arrive, chasing away the vampires.

Across the field, Shinoa tells Guren she has questions for him, but he says he will not answer them.

Post-Shinjuku Arc
Shinoa spends five days hunting him down before finding him in a lab underground. She tells him that Yu has not woken up since his transformation. Shinoa asks him what she did to Yu, and she reveals that she gave Yu different supplements than the other members of her squad. Guren refuses to give any direct answers. He states that Shinoa's sister, Mahiru, invented Cursed Gear. He says that sacrifices are necessary and scolds her for her idealism. Guren then asks her if she has a crush on Yu, and states that he does not care. He orders Shinoa to leave. He informs her that the drugs wear off after five days, so Yu should wake up soon.

In chapter 16, Guren waits for Yu while Yu heads to meet with the higher ups. Guren asks him if he is wagging his tail for the main family like a good mutt. he realizes Guren does not get along with the upper brass. Guren reminds Yu that he saved Yu, taught Yu how to live here, and taught him how to use a sword. He tells Yu that he is alive because of him. Yu is his and belongs to his faction. So Yu shouldn't go wagging his mutt tail to the Hīragi.

Yu tells him does not care about his stupid politics and says he will never abandon or betray his friends ever again, so Guren should quit worrying. Guren says that he is not Yu's friend but rather his superior, savior, surrogate father, and adding all those things up, practically a god to him. Guren says Yu can call him "papa," but Yu declines.

While Yu attends his meeting, Guren meets with the demon Mahiru within his mind. When Yu exits with an injured Yoichi and Kimizuki, he yells at Guren to teach him the proper way to use his Cursed Gear.

Guren meets with Shinoa and Yu before the actual squad meeting. As he saw them holding hands, he sarcastically asks if their gonna skip off to make out. Yu counters by saying that Guren is late. Yawning, he tells Yu to shut up as he was up all night in stupid army meetings. He tells Yu that he's tired and in a foul mood and asks if he can go home and Yu promptly tells him no. He claims that both Mitsuba and Shinoa can teach them how to use their weapons properly. Shinoa manifests Shikama Doji and explains that manifested demons can use special abilities. Yu asks Guren if he could do that with Asuramaru. Guren tells him that it depends on the type of demon he is. There are some like Shinoa's demon and then there's the type of demon that directly possesses the user to grant immense physical strength. He says his blade is the latter.

Guren challenges Yu to a fight to see if he's ready for the next step. He tells Yu to draw and activate his sword and he'll only do a normal activation. Yu is excited, stating that's it's been a long time since their last spar. They spar and Yu asks him if he's gonna compliment him on his skills as he says that the gap between them isn't as big as before. Guren says that it's only due to using only standard activation. He says next he'll have his demon possess him. He orders Mahiru to possess him. He tells Yu that if he can take one hit then he'll get his compliment. He then promptly flings Yu from the rooftop.

After hearing Guren summon his demon by calling out her name, Shinoa holds her scythe at Guren's neck. She reveals that her weapon specializes in long-range combat and consequently stands no chance against a melee fighter like Guren at that range. Guren calmly says he would let Shinoa kill him. Shinoa asks him if that is his way to atone for killing her sister, Mahiru. She asks if she is in his sword since she heard him call her name. Guren says that Mahiru is already gone since she turned into a demon and saved the world by completing Cursed Gear. Shinoa laughs, stating that Mahiru was never one to care about the world because she loved him. She longed to be with him since they could never be together and became obsessed with demons.

After discussing the events of eight year, Shinoa says that if Mahiru hadn't completed the development of Cursed Gear, humanity would have perished. Her sister, who was just a girl in love became something like a Messiah. But then she was killed when she became obsessed with her research and became a demon. She continues saying, the one who killed Mahiru was the person who used to be her lover, him, Guren.

Shinoa asks him if Mahiru is together with him inside his sword, stating that he is being possessed by her. Guren asks her if she and Mahiru ever got along. She explains that she was not close with her sister because Hīragi's are raised without knowing familial love. He tells her to shut up and drop it.

Shinoa then tells him that watching a "certain someone" get so desperate to save someone he has no blood ties to has made her wonder if she should put more value into "friendship" and "camaraderie". From that she asks if making use of Yu was one of Mahiru's orders and asks if her sister or the demon for lack of a better word that is inside his sword is ordering him. She asks what his goal is, though he doesn't say anything. As if warning him, she asks that if his goal is something that does not benefit Yu, that she'd appreciate if he stopped. Guren sighs and asks if she seriously is head over heels for him.

Yu slams open the door, yelling that he's back and tells them that he tried climbing up the building with his sword. He wants Guren to teach him how he did that with his demon. As Yu and Shinoa chat. Guren sheathes his sword and thinks that

The rest of the squad arrives half an hour early, interrupting their meeting.

Guren tells her that Mahiru is dead and isn't coming back. He says that the demon inside his sword is under control so he isn't being possessed by her. But Shinoa doesn't believe him. He orders Mitsuba and Shinoa to advance the training of the three new recruits before heading elsewhere for a nap. Before he leaves, Yu asks if he and Mika were really guinea pigs used by the Hyakuya sect for human experimentation. He asks if Guren rescued him in order to use him. Guren answers that he has no time or resources to rescue those he cannot use. He asks if Yu is mad at him but Yu tells him that whater his reasons, he would have died if Guren hadn't rescued him; he feels that he owes him. Yu wants to know if he himself is useful to him. He doesn't care about the fight between Guren and Kureto is, all he wants to know is if Guren needs him. If he does, would he want Mika as well and if so, he will be Guren's guinea pig or anything he wants. He'll do whatever he can to help him; all he wants is to get Mika back. Guren says that everyone standing there is family, including him. Family works together to bring family back. He finally leaves to go home and sleep.

Nagoya Arc
In chapter 23, Guren meets with Kureto Hīragi. He walks up toward where Kureto oversees five chained and starving vampires. Kureto claims he is testing to see if he can force vampires into becoming demons, so they can create Cursed Gear more efficiently. He claims that most of the low-level vampires do not turn, and those that do turn become weapons even weaker than the replicas of the stronger weapons. Kureto orders them killed and steps down to speak with Guren. They bicker a little, and Kureto asks Guren how he created so many Cursed Gear users (Yu, Yoichi, and Kimizuki). Guren starts saying that he just got lucky, but Kureto says that every single human capable of bearing a Black Demon has been a human experiment at one point. Even with the experimentation, the chance a candidate is successful is slim. The fact that Guren managed to create three of them, all successful, is extremely impressive. Instead of pressing the issue, Kureto tells him that success is a boon and asks that he share his experiments with them if more are successful. Kureto then asks Guren if he is planning a coup. They reminisce briefly on their high school days. Kureto calls Guren out on what he sees as Guren's weak point: no matter what happens, he claims that Guren cannot betray his friends. He says this weakness is why Guren is unworthy of being a leader and also why he trusts Guren. Guren asks him what hostage Kureto prepared this time, but Kureto says he was too busy. Kureto asks Guren about his vision. Kureto announces his dream of eradicating all vampires in Japan, then crushing all other surviving human organizations, and finally uniting the world under the Japanese Imperial Demon Army.

Kureto then gives him orders to lead a pre-emptive strike with 100 soldiers on the vampires in Nagoya. Guren calls it out on being a suicide mission, but Kureto claims it is a vital mission instead.

Proceeding with the mission, Guren waits for his troops to arrive at the Ebina rest stop prior to leading the strike on Nagoya. While his squad messes around, Shinya arrives unannounced to give Guren a hand. He also believes this is a suicide mission. He gives a brief speech to his squad, causing Sayuri, Shigure, and Mito to blush. When Goshi and Shinya tease him for giving the speech on a sports car, he manages to hit Goshi and orders Sayuri and Shigure to get him a different stage. When Shinoa's squad arrives late, he scolds them vehemently. Yu takes the blame, and Guren promises to punish him later, even though he knows Yu is covering for Shinoa.

Guren gives a speech to the Moon Demon Company, and Shigure hands out orders for the individual squads.

At the Ebina rest stop, he summons Yu for his punishment. They chat, and Guren tells him he is glad about Yu's attitude change. Yu also chats with the rest of Guren's squad, finally realizing that Sayuri is his teacher. He recognizes Shinya as well. Moving on, Guren orders Goshi to create a mortifying illusion of a naked Yu screaming for his mommy. Hearing his screaming, the rest of Shinoa's squad charges in, and she breaks the illusion.

After scolding her, he challenges her to a match: Guren, Mito, and Shinya against her entire squad. He gives her ten seconds to prepare.

Guren strikes off against Yu, quickly distracting him with an explosion ward and getting past him to strike Mitsuba and Shinoa. He lectures him. This exercise teaches Shinoa's squad a lesson, helps Shinoa's squad gain focus, shows off the strength of the newbies as three wielders of the Black Demon Series, and raises moral of the troops.

Beginning their mission in Nagoya, Guren's squad charges underground, eliminating vampires as they go. He assigns three squads to each of the eight nobles they are targeting. Shinoa and Narumi's squad are the only group to have only two squads, and he leaves Shinya with them to take over command if something happens to Guren. Guren's squad takes on Nineteenth Progenitor Mel Stefano on their own. Although they succeed, Guren and his squad are pretty bruised and battered. His squad claims he nearly died eight times in that fight, and they decide to use at least two squads in their next attack.

A soldier named Kusunoki reaches Guren, collapsing to the ground and giving him information. He says ten soldiers were killed and another twenty are hostage in Nagoya City Hall. This means that six squads were exterminated while hunting their two vampire targets. Even though this is an obvious trap, Guren's squad goes to reinforce Shinoa and Narumi's squad. He adds a new target to their list: Thirteenth Progenitor Crowley Eusford.

When the Moon Demon Company regroups, he asks Narumi for a report on rookies' teamwork, and Narumi tells them they did very well. Sergeant Aiko Aihara reports that she lost 8/15 of her team, and Guren tells her that is not her fault. Guren orders Narumi Squad and Shinoa Squad to accompany him in exterminating Thirteenth Progenitor Crowley Eusford, Seventeenth Progenitor Chess Belle, and Seventeenth Progenitor Horn Skuld and rescuing their comrades. Shinya asks him if he is okay after losing so many people today, and Guren says he will just cry later. He informs the squads they will only attack for ten minutes. He orders Aiko to wait half an hour for other squads and to send them to Nagoya Airport.

Once they reach Nagoya City Hall, Guren looks at the hostages being used through a telescope and knows that they are being used as bait to lure them. Yu insists on bursting in and saving them. Narumi dismisses it as too dangerous and when Yu asks him what they should do, Narumi asks Guren what they should do. Guren suggests that they snipe them from their position and see if they can lure them out but says that if there are too many of them, they are to abandon the hostages and run. Yu shouts that they can't do that.

Shinoa interrupts Yu and asks Guren what their priorities are. In order, he says that their top priority is to maintain their numbers, letting no one die. Their second priority is to free the hostages and lastly, getting the hostages out alive. Narumi states that this is because they are needed for another mission after this. Guren then says that they need to keep the vampires occupied in Aichi Prefecture for as long as they can so they can buy enough time for the main forces in Shibuya to get prepared.

He says that once the hostages are free, they need to draw as much attention to themselves as they can and then begin their next mission which is to survive as long as possible. Shinya says that essentially, the plan to actually make alot of commotion only to run away in the end. Guren says that's right and if it goes well, the squads that are finished with their assassination mission will hear the commotion and find them and then they'll kill the vampires holed up in city hall.

After Crowley catches Gekkōin, Guren and his squad discuss what to do while Crowley, Horn Skuld, and the Seventeenth Progenitor Chess Belle wait patiently for them. After careful planning, Guren decides that his squad will take his squad to attack Crowley while Shinoa and Narumi Squads free the hostages. He gives them five minutes to rescue as many hostages as they can and act as a proper diversion for the main force in Shinjuku. As soon as the five minutes are up everyone has orders to retreat to the Nagoya Airport immediately.

Guren and Shinya attack Crowley at the same time but he easily negates their attacks at close range. He then swings Guren into Shinya, throwing them into the wall behind them. Crowley, Chess, and Horn then step toward them. Mito notices this and moves to assist them but Goshi holds her back and tells her, she would only get in the way.

Sometime later, Yoichi reports on this situation with Guren's squad to his squad and Yu insists on rescuing him. Shinoa agrees with him but says they only have five minutes. She gives them specific instructions regarding their plan. When Shinya and Guren attempt to flee from Crowlely, Chess, and Horn, Shinoa Squad breaks through the floor below, and Yu attacks Crowley. The vampires easily block and counter the humans' attacks.

Guren orders them to escape, and Shinya agrees. Shinoa orders Yu to leave as well. Guren calls Goshi out of hiding, and Guren's personal squad breaks in through the windows. Goshi creates an illusion, allowing the humans to escape, but they are forced to leave Guren behind.

Crowley orders Chess and Horn to restrain Guren and take him with him.

After Yu rushes off and challenges Crowley, Guren, whose wrists have been bound, gets between Yu and Crowley and orders Yu to leave because Crowley is more powerful than any other vampire he’s fought. When Yu asks why he is still not strong enough, Crowley answers that it is because Yu is only livestock and asks if Yu fears cows and pigs revolting someday. He insists vampires will never fear humans. Yu repeatedly yells at him to shut up and die, and they exchange blows. Guren orders Yu to stop. He says that Yu's demon will take over if he uses more power than that. He calls Yu a stupid brat as he told him that he’s already done for and Yu should abandon him and run. Yu yells at him not to not dare give up as Guren was the one who told him to live despite all the pain. Yu tells him to be a good adult and be a good example for him.

Crowley mutters that he is beginning to get bored and even though Yu is a key part of some silly little human plot, he’ll kill him. Yu tells him that he’ll never give up. Guren tells Yu that he has a plan, but Yu needs to leave. Yu does not listens and demands even more power from Asuramaru. Guren tries to stop him, telling him not to let his desires swallow him. Yu's desires overwhelm him, and half of his face darkens and a horn sprouts from his head as he becomes a demon.

Yu challenges Crowley again. Kimizuki appears behind him, telling Kiseki-Ō to begin the count to nine until the devil's coffin opens. After Kiseki-Ō gets to four, Yu invites Kimizuki to kill this bloodsucker together, but Kimizuki notices Yu's horn. Guren warns Kimizuki that Yu has been possessed and he’s lost all control of himself. He tells Kimizuki to grab him and run. Yu tells Guren to shut up now that he has the power to rescue him. Kiseki-Ō finishes the countdown and captures Yu with the devil's coffin.

Guren shouts that his final order to them is to live and escape..

The captured Guren is next seen in chapter 38, bound and kneeling before a pink-haired vampire girl, flanked by three imposing bodyguards. As he pondered his fate, he recalled the words Yu spoke to him earlier, about how he was the one who told him to live despite all the pain, and to be a good example of an adult for him. "Stupid loud-mouthed brat," the soldier grumbled, as an unnamed noble approached him. Privately, a silent voice told him not to let the fear win and resist a little, since vampires didn't kill their "livestock" all willy nilly. As he felt his hair grabbed, the same voice told him to give them a little info to lure them into Shinjuku, and Kureto would do the rest. The noble commanded him to tremble in fear, incensed that he'd "laid his hands on nobility," and wouldn't get away with it. Guren spat at the arrogant vampire, which earned him a hard roundhouse kick to the face, sending him flying across the street. The vampire angrily vowed to kill him, and viciously assaulted him for what he'd done.

As Guren laid on his back, he wondered when did getting assaulted become so exhausting. Regardless, he felt he should suffer a few more blows to make his testimony more convincing. He then laid facedown on the street, his assailant demanding answers else he'd forfeit his life. Guren finally mentioned Shinjuku, as his katana extricated itself from its sheath. As it did, a change came over Guren, who threatened to kill the noble if he laid his hands on him again. Before the vampire could respond, the blade neatly sliced off the noble's head, and Guren freed himself from his bonds, the twisted image of his beloved hovering above him. Krul claimed to be unimpressed, so Guren aimed his sword at her, demanding her assistance in an Owari no Serafu experiment. The child-like vampire realized he was connected to Mahiru.

Natural Abilities
Guren is an intelligent scientist, capable of developing Cursed Gear. He even created a method with a very high rate of success for the development of humans who can bear Black Demon Series weaponry. Later, it is revealed these humans are actually the seraph he secretly collected after the Hyakuya's downfall.

He proves himself as a capable swordsman, strategist, and leader on the battlefield. He is rumored to have even recaptured Shinjuku from the vampires with a single team.

Magic and Spells

 * Fudo Myo-o Spell: Guren is capable of using enchantments on spell tags. In particular, this is an ancient one that causes an explosion after a few seconds. Guren uses this as a distraction in his battles against Yu and Mika.

Cursed Gear

 * Mahiru-no-Yo 「真昼ノ夜, lit. Midday's Night」: A possession-type demon weapon of the Black Demon series. It takes the form of a black katana. The demon inside was originally a human named Mahiru Hīragi, his former lover, whose research eventually turned her into a demon until Guren himself killed her.

Trivia
Shinya: ''"Guren is a pretty shy person. Although he really likes us, he’s not very straightforward about it." ''
 * The writer, Takaya Kagami, thinks of Guren as "The Unparalleled Ichinose!" while writing him.
 * Guren 「紅蓮」 means "crimson lotus."
 * Ichinose 「一瀬」 means "one rapid."
 * He is one of the first characters designed, along with Mikaela and Yūichirō.
 * In chapter 14, Kureto promises to give Guren a reward for his efforts in Shinjuku. It turned out to be chocolate ice cream.
 * According to the fanbook:
 * Interests and Likes: [Interests] Yūichirō / Mahiru [Likes] Games / Jazz
 * Favorite food: Curry
 * What he looks for in the opposite sex: Mahiru Hīragi
 * Comments about him:

Kureto: "That guy works well. He appears to be doing something under cover, but I’m planning to capture him as a hostage for now."

Light Novel

 * "To me, who was lowly born, she was the sun...."-- Guren about Mahiru. Volume 1, prologue.

Manga

 * "There he is. Just like the prophecy said. One of the lab rats from Hyakuya Laboratories, the company that destroyed Japan. Boy. You are going to be of use to me in exterminating vampires."--Guren to 12-year-old Yu after escaping Sanguinem, Chapter 1, "The World of Blood Legacy"
 * "Sorry, Kid. The army doesn't have use for virgins who are too scared to work in a team, make friends, or date. If you want in, then make a friend at that school and introduce them to me. I'm not holding my breath. YOU FAIL!"--A note from Guren to Yu, Chapter 2, "Humanity After the Fall"
 * "Quit screeching. Nobody wants to hear it, Vampire."--Guren to the escaped vampire, Chapter 2, "Humanity After the Fall"
 * "Nope. I hate brats who don't know what 'teamwork' means."--Guren rejecting Yūichirō from joining the Moon Demon Company, Chapter 2, "Humanity After the Fall"
 * "Okay, listen up. The reason that I, your homeroom teacher, decided to grace you all with my presence today is because we have two transfer students... Anyway, here they are. Yūichirō Hyakuya and Yoichi Saotome. They're the idiot and the crybaby, respectively. As of today, they're joining your class."--Guren to the Moon Demon Company classroom, Chapter 4, "The Worst Pair"
 * "Leave 'em. We won't get anything done in class with them conscious. Right then. The Cursed Gear aptitude test is coming up in a week. It's been a while, but I guess I'd better teach you guys something, eh?"--Guren to the Moon Demon Company classroom after pulverizing Yūichirō and Kimizuki, Chapter 4, "The Worst Pair"
 * "That doesn't matter. Strength alone is not enough. Make friends. Find companions. Don't try to handle everything by yourself. Because if you do... when the demon sinks its claws into you... it will swallow you whole, and you won't be able to come back. Anger and impatience are a demon's favorite snacks. As you are now... you'd be devoured by your own desires and turn into a demon yourself."--Guren to Kimizuki, Chapter 4, "The Worst Pair"
 * "I guess it's time I started making some preparations to steal the throne of this little kingdom out from under the main family."--Guren to Shinoa, Chapter 4, "The Worst Pair"
 * "Oh, I most humbly beg your pardon, General Tenri Hīragi. It's just that I was bored out of my mind."--Guren to Tenri Hīragi, Chapter 5, "Vampire Mikaela"
 * "Ugh! Dealing with idiots can be so exhausting. Still... Things are about to get a little more interesting."--Guren to Tenri Hīragi, Chapter 5, "Vampire Mikaela"
 * "If you're not strong enough, you die. That's the way the world works now. We aren't holding hands and playing house here."--Guren to Sayuri, Chapter 6, "Black Asuramaru"
 * "Well, damn. I guess Yoichi wasn't quite strong enough after all. Still... A two-out-of-three success rate with the Black Demon Series is pretty good."--Guren to Yūichirō and co., Chapter 6, "Black Asuramaru"
 * Okay, you two have your Cursed Gear now, so here's your first official Moon Demon Company mission. Yūichirō. Kimizuki. Look at the ceiling. There's a man-eating demon up there. You two go kill it."--Guren to Yu and Kimizuki, ordering them to kill Yoichi, Chapter 6, "Black Asuramaru"
 * "YOICHI! Are you going to hide underneath that bed and watch your family die again?! Get out of here and protect them!"--Guren to a possessed Yoichi, Chapter 7, "New Family"
 * "You have talent. But you feel guilty because you couldn't save your sister. That's sapping your desire to live. But today... you've found enough reason. Your reason to live now... is to protect the ones who saved you today. Your friends. Revenge? Don't let something so petty consume you. That goes for you too, Moron. Forget your old family. Because you have a new family now. Put your life on the line for the ones you see before you. The past is gone. There is only the future."--Guren to Yoichi, Yu, and Kimizuki, Chapter 7, "New Family"
 * "Sheesh. Raising kids is exhausting."--Guren to himself, Chapter 7, "New Family"
 * "Oops. I missed their commander. Ah well. Once we control this point, we'll have have won anyway. Hey, Vampires! Was all that human blood you drank today tasty? Sure hope so... because that was your last supper. Here we go. Give me more power, Demon Blade: 'Mahiru-no-Yo.'"Guren's pre-battle speech, Chapter 11, "Queen's Contract"
 * "Oh ho! You're a strong one!"--Guren to Mikaela Hyakuya, Chapter 12, "A Very Safe Supplement"
 * "Over here. Checkmate, Vampire."--Guren to Mikaela Hyakuya after trapping him, Chapter 12, "A Very Safe Supplement"
 * "Thanks for your patience. Mind if I ask you to wait just a bit longer, though? It's time for us to take our medicine, see. Do you mind giving us, oh... another 20 seconds or so?"--Guren to Mikaela Hyakuya after reevaluating Mika and Ferid's strength, Chapter 12, "A Very Safe Supplement"
 * "So then, if I told you we're using him in our experiments, would you be angry? Humans are weak. Fragile. Now that the world has ended, what do we have to do to survive? What do we have to do to kill vampires? To eradicate the horsemen? Your sister, Mahiru Hīragi, invented Cursed Gear. How many people were sacrificed in that long process? Without it... do you honestly think humanity would be able to survive? Understand? So quit spewing idealistic crap at me, Little Girl. Or, what... Are you falling in love with Yūichirō?"--Guren to Shinoa about Yūichirō, Chapter 14, "Everyone's a Sinner"
 * "Yūichirō. You remember, right? Who the one who saved you was. Me. Don't forget who was there for you when you came crawling out of the vampire capital. Me. I went out of my way to teach you how to live here. Even how to use a sword. If you feel like you owe me at all, then pay me back today. You live because of me. You are mine. You belong... to my faction. So don't go wagging your mutt tail to the Hīragi."--Guren to Yu, Chapter 16, "Human World"
 * "You're wrong about one thing, though. I'm not your friend. [I am] your superior. The guy you owe your life to. Your surrogate father. Put all those together, and I'm practically a god to you. You can even call me 'papa' if you want."--Guren to Yu, Chapter 16, "Human World"
 * "Sheesh. Did you have to go on a stupid rant about the obvious, you idiot? I already told you... Everyone standing here right now is family. That includes me. Family... works together to bring back family."--Guren to Yu and their squad about Mika, Chapter 18, "Possessed by Mahiru"
 * "So now is the part where you show off your special hostage? Who is it this time? Are you going to torture Shigure, Sayuri, or any of my other aides in front of me?"--Guren to Kureto, Chapter 23, "Ambition in the Demon Army"
 * "Shaddap. I'm not that dumb. I'm scared of who I could lose on this mission. But... we have to answer the call. If we fail, humanity dies. And so, Shinya. Goshi. Mito. Sayuri. Shigure. I want to complete this mission with as few casualties as possible. For that, I ask for your help."--Guren to his squad and Shinya, Chapter 24, "The Moon Demon's Orders"
 * "SHUT YOUR MOUTH, CHILD! This mission is not a game!! If you can't follow even basic regulations, we don't need you! Go home!"--Guren to Shinoa in front of the Moon Demon Company when her squad arrives late, Chapter 24, "The Moon Demon's Orders"
 * "Listen up, everyone. During this mission, I will have zero tolerance for anyone who doesn't follow regulations. Nor will I tolerate anyone treating this like a game or messing around. I repeat, this is not a game. This is the most difficult, dangerous mission we have ever undertaken. Some of us are going to die. We are all family here. And on this mission, we are going to lose a lot of family members. But despite that danger, this is a mission worth risking our lives for! Listen up!! I don't want us just coming home alive... We will come home victorious!! DO YOU HEAR ME?!"--Guren to the Moon Demon Company, Chapter 24, "The Moon Demon's Orders"
 * "It's your punishment. Shinoa. This is your squad. I'm doing you a favor and teaching you that even a little mistake could kill them.... You don't get it. You've never had anyone important to you before. You don't know what it's like to fear losing someone. But now things are different. Even a tiny mistake is enough to kill. Your little pranks could cost your family their lives."--Guren to Shinoa, Chapter 25, "Narumi & The 20-Year-Old Yu"
 * "You have three Black Demon wielders on our team. What the hell was that? You showed very little teamwork. The vampire nobles we'll be facing are stronger than us three. How do you expect to fight them? Or do you plan on standing there, cracking snarky jokes while you die?"--Guren to Shinoa's squad, Chapter 26, "Thirst Logic"
 * "We're going to reinforce Shinoa Squad and Narumi Squad. Once we do that, I'm adding a new target to our list. He's currently located in the Nagoya City Hall. We are going to kill... Thirteenth Progenitor Crowley Eusford."--Guren to his squad, Chapter 28, "Livestock Revolt"
 * "Anyone with a heart cries when a friend dies. But we can't afford to do that right now. We have a mission to complete."--Guren to Shinya, Chapter 29, "Who's Pulling the Strings?"
 * "You idiots!! Why the hell did you come?!  Follow your orders, dammit!!  Get out of here now!!"--Guren to Shinoa Squad, Chapter 33, "Demon's Lullaby"
 * "I'm already done for... Save your strength for getting Shinya and the others out of here."--Guren to Norito Goshi, Guren Squad, and Shinoa Squad, Chapter 33, "Demon's Lullaby"