Kiseki-o

Kiseki-o (鬼箱王) is a high-ranked possession-type demon of the Black Demon Series. He formed a contract with Shihō Kimizuki and became his Cursed Gear. His weapon form is two twin blades connected by a cord on the hilts.

Appearance
He appears as an androgynous preteen. He has short light green hair with short bangs and short eyebrows. He has red eyes, pointed ears, fangs, black horns as long as his forearm (only after he drinks Kimizuki's blood), and a fluffy white tail as long as he is tall. He wears a black headband behind his horns and a dangling earring with a sapphire orb on his right ear.

Kiseki-o is dressed in a white sleeveless collared shirt with a black knot with a brown belt and short black shorts. He wears black cuffs on his forearms, matching socks that reach up to a few inches below his knees, and black boots with heels that he leaves unzipped halfway.

He often takes the image of Kimizuki's younger sister, Mirai, while battling him for control.
 * Anime: In the anime, his horns are dark blue and his earring orb, belt, cuffs, and boots are purple.

Personality
As a possession-type demon, Kiseki-o is particularly proud and nasty, and he is utterly unwilling to surrender to the weak. He uses the memories of Kimizuki's sister against him to break his will.

Unlike Yūichirō Hyakuya and Asuramaru, Kimizuki must assert his dominance through violence. Despite the way he acts, Kiseki-o claims to like Kimizuki. This does not stop him from insulting Kimizuki as pathetic and questions if he has been rendered speechless by his inadequacy. Although condescending and capitalizing on moments to make Kimizuki feel worse such as happily agreeing that he saw Kimizuki was too weak to save his sister, Kiseki-o is able to provide clear guidance on what he wants Kimizuki to do.

History
Kiseki-o is a demon who was sealed within Cursed Gear in the form of twin swords connected by chains.

Second Shibuya High Arc
Although Kiseki-o does not actually appear, he takes the form of Mirai and uses an environment of Kimizuki interacting with his sister from the past. He begins with speaking pleasantly, replying as Mirai that she is not too bad and thinks it is going to be a good day for them, before asking why her brother does not leave Mirai to fend for herself so he can move on with his life. Saying if things do not change Kimizuki will end up dead too, as Mirai she answers that Kimuzuki does not really mean that he intends to have them both survive. At that point Kiseki-o drops the pretence of acting like a sweet girl, yet still as Mirai he darkly speaks that Kimizuki wishes Mirai would just die already. Rising from bed, Kiseki-o states that despite how noble Kimizuki tries to be, deep down he is a selfish human who only thinks of himself. Kiseki-o confirms that he is the demon, and questions whether he was right about Kimizuki's thoughts. He has seen every shameful thing that has floated through his little brain and wonders what his sister would say if she knew the truth. Aware of it, he matches Mirai's concern that Kimizuki forges a contract with him in chapter 6 and does so faster than Yūichirō and Asuramaru.

Post-Shinjuku Arc
In chapter 21, Kimizuki advances his training with Kiseki-o, and they battle for over 30 hours. Shihō screams and shakes as they fight within his mind. Shinoa warns her squad to be prepared to eliminate Kimizuki if he loses control. In Kimizuki's mind, he struggles against Kiseki-o, who taunts and then stabs him, catching Kimizuki's blood in his mouth. He insists that Kimizuki's body is already his and bites him, commanding him to break and sending him into his illusion. Kimizuki relives his past of four years ago when he was eleven years old. Mirai says to leave her behind, and Kimizuki realizes this is an illusion once again. Kiseki-o corrects him, saying that these are his true memories and insisting that he wanted to abandon his sister.

Three other kids around Kimizuki's age come to his apartment door and say it's time to move. They try to convince him to kill Mirai, who is an invalid and is always holding them back. They say she told him she wanted this. When he refuses to, they say they will do it for him. He breaks free and locks them outside of the apartment. Mirai insists on Kimizuki killing her, and Kimizuki keeps telling her to shut up. The demon reveals his deepest desires, insisting he resents taking care of Mirai and wondering why this all happened to him. Kimizuki approaches Mirai and begins chatting about Yu. He says Yu wants to rescue his family no matter what, even though they aren't blood related. Kimizuki says that if the only solution is to kill his sister, then he will choose death. He insists he will never do what the demon says and stabs himself to break free.

Recovered from the psychic wounds, he charges at Kiseki-o and cuts him. Kiseki-o says there is still darkness in Kimizuki enough to betray his friends if it meant saving his sister. Kimizuki insists there is no one without darkness in this world, and Kiseki-o smiles. He says he likes humans and Kimizuki and decides to lend Kimizuki his power.

Kiseki-o later pays attention when Kimizuki and Yu start fighting, where Yu had the upper hand and Kimizuki started losing. As he saw Kimizuki was just as pathetic as always. He keeps screaming a desire to save his sister and begging him to grant more power but Kimizuki does it for show. Kiseki-o adds further that Kimizuki is not desperate enough and is not nearly as insane as his opponent which it why he is weaker than Yu. In addition deep in Kimizuki's heart he truly given up on his sister. All he really wanted was a peaceful life with friends and have fun and Kiseki-o queries what is wrong with the nice dream. Kiseki-o finds him dull as he was speechless and wonders if Kimizuki was rendered speechless by his own inadequacy. Agreeing having seen it that Kimizuki was too weak to save his sister Kiseki-o would not say it is all bad that Kimizuki is justifying excuses not to try. Placing a hand on his shouler Kiseki-o has watched Kiizuki, observing from inside him this whole time. Judging him a very rational person and caring for his friends Kiseki-o continues to say that Kimizuki always tries to help everyone but this results in him losing sight of his own desires.

Asked what Kimizuki desires Kiseki-o answers he have to figure it out himself and not to ask him whether Kimizuki is weak because he has not. Kiseki-o wants to hear Kimizuki's soul and voice, to forget about his sister and friends. He wants Kimizuki's selfish, childish ugly desires. As Kimizuki cries, that he is sick of it, wanting to win and he cannot stand Yu showing him up all the time Kiseki-o sees it and asserts that Kimizuki can do it. It is the first time Kimizuki has really opened his heart to him and the walls his logic put up are finally coming down. Placing his hand in Kimizuki's chest Kiseki-o can now give him power. Guiding him to forget about his sister, friends, and his responsibilities Kiseki-o wants Kimizuki to tell him he wants more for him to give it. The twin coffins power is able to be summoned. Later Kiseki-o relaxes in a coffin with the lid open in his realm and notices Asuramaru. Greeting him he wonders whether his memories have finally come back too as it seems that the king has finally awakened.

Powers and Abilities

 * Demon's thrall: Kiseki-o can enter his host's dreams and memories to create nightmares and break his host's will. This is done in order to take over his body. This ability can only be used against his host.
 * Basic form: Connected with a pair of twin swords are Kiseki-o's most basic form. He gives his bearer great strength and power. By calling his name, he gives his bearer even greater power. A melee-type weapon.
 * The Devil's Coffin: Kiseki-o's special ability involves manifesting and opening the devil's coffin on the count of nine. Anyone who hears the counting at a close distance will be forcefully captured into the devil's coffin upon reaching nine. Yu claims to get very bad vibes from it and believes it to be something really nasty. This type of ability should be impossible for a possession-type demon.
 * Twin Coffins: An enhanced version of the original ability, but instead of one coffin, two can be summoned instantaneously, They appear in close range on either side at the target. Instead of the count to nine, this technique does not require counting. Instead it fires a barrage of spiked dark projectiles at close range.

Shihō Kimizuki
A special private in the JIDA, under the Moon Demon Company, whom Kiseki-o forms a contract with. He describes Kimizuki as ugly, young, and naive, but he claims to like him. Their battle for control can be violent with Kimizuki asserting his control through sheer power. He often creates illusions with Kimizuki's sister Mirai in order to break Shiho's will. When Kimizuki is failing in his sparring against Yu, Kiseki-o invites himself into the matter to voice that Kimizuki shouts a desire to protect Mirai as a show. In reality he has given up on Mirai of which Kiseki-o understands that it is a nice dream for Kimizuki to just want to live peacefully and have fun with friends. Whilst he articulates Kimizuki's inner conflicts Kiseki-o says that Kimizuki has to figure out his desires and to not ask him. Some pointers are that he does not not need the thoughts of a rational adult as Kiseki-o encourages him to embrace selfish desires. Having identified logic as a wall around Kimizuki he wants him to forget his sister, friends and responsibilities.

Yūichirō Hyakuya
Kiseki-o used his ability to restrain Yu from being overtaken by his demon. Using the Devil's coffin ability was sufficient in achieving this purpose, causing Yu to fall unconscious and nullify Asuramaru's influence. Kiseki-o feels Yu is stronger than Kimizuki because he is more desperate and insane.

Mirai Kimizuki
Shiho Kimizuki's ill younger sister. She was infected by the Apocalypse Virus even though she was younger than 13, and Kimizuki has taken care of her since then. This has been very stressful for Shiho, and she even wanted Shiho to kill her back then. She is currently under JIDA's care. Kiseki-o is fully aware of and exploits their connection, often taking her form to torment Shiho. He wondered what Mirai would say if she knew the truth of Kimizuki's thoughts.

Asuramaru
At seeing Yu's demon in his realm Kiseki-o greeted him and questioned whether he too had at last regained his memories.

Quotes
"La la. La de dah de dah. Well now, Shihō Kimizuki. Would you like to give up?"

- Kiseki-o to Kimizuki.

"I do not submit to the weak."

- Kiseki-o to Shihō Kimizuki

"This is the end, Human. Relive your past. See your inner darkness. Look at your deepest, ugliest desires. Let 'Shihō Kimizuki' break."

- Kiseki-o to Kimizuki.

"There, see? For a moment, you wished you could end it all. You were sick of it. You wondered why all this had to happen to you. You were only a child, after all. It was hard. You were scared. You wanted someone to save you. You wanted to run away from it all, forever. If only you had actually killed your sister... If only you had rid yourself of that burden... Wouldn't it have been better? Yes... That's exactly what you thought, isn't it? It is over, Shihō Kimizuki. You failed at life that day, when you made the decision you did. There's no need to be stubborn. Take the easy path. It's simple. Just take that knife and do what you should have done then. Come on. Put your sister out of her misery."

- Kiseki-o to Kimizuki.

"...Ah well. There is no rush. After all, there is still darkness inside of you. Darkness so deep you wouldn't hesitate to betray your friends if it meant saving your sister."

- Kiseki-o to Kimizuki.

"Yes... That's right. That's why I like humans. And I like you too. I guess I could lend you my power. You are ugly, young and naïve... but you may call upon me to possess you."

- Kiseki-o to Kimizuki.

"Our prey is caught! Now, kill it! KILL! KILL! KILL! KILL! KILL! KILL! KILL! KILL!"

- Kiseki-o to Kimizuki after capturing Yu in his coffin.

"You aren't nearly as insane as him. That's why you're weaker than him."

- Feeling that Kimizuki is weaker than Yu and why

"Deep in your heart... ...You've given up on your sister"

- After addressing how Kimizuki keeps screaming that he is going to save his sister, for show.

"All you really want is a peaceful life. To hang out with friends. To mess around and have fun. And what's wrong with that? It's a nice dream."

- Voicing what Kimizuki really desires and in favour of it.

"You're a very rational person. You care a lot about your friends. You always try to be the one adult in the room... ...helping everyone else. But because of that... ...you lose sight of your own desires."

- Appraising Kimizuki's character and his behaviour around others.

"Let me hear your soul. Forget your sister. Forget your friends. I want your selfish, childish, ugly desires. I want to hear your voice."

- At his level Kiseki-o guides Kimizuki.

"That's the first time you've really opened your heart to me. The walls your logic put up are finally coming down."

- Making his own progress and knowing logic as the barrier in the way.

Trivia

 * In Japan, characters like Kiseki-o are considered to be masculine on facial appearance, as a common Japanese myth and element is that young-male demons are baby-faced which would appear rather effeminate elsewhere.