Byakkomaru

Byakomaru (白虎丸) is a high-ranked manifestation-type demon of the Black Demon Series. He formed a contract with Shinya Hīragi and became his Cursed Gear.

Appearance
Byakomaru's weapon takes on the form of a black, green striped sniping rifle with a bayonet attached at the end. It can either fire off a rapid succession of projectiles or fire a single bullet to manifest Byakomaru.

Byakomaru manifests as a gigantic white tiger, surrounded by bright blue flames. The tiger can split into multiple tigers in manifestation form to strike down its targets.
 * In the anime, the bayonet has been shown pointed downward to help support the rifle while Shinya is sniping.

In Chapter 83, Byakomaru is shown to have a human form. His human form wears a white tiger pelt headdress that covers the top half of his face. Like all former vampires, he has red eyes (which aren't always visible) and fangs but it's unknown if he has pointed ears (though it's very likely he does). Along with that, he wears a longish Japanese style vest over a black shirt with long, small, flowing sleeves and black pants. Finally, he wears longish black gloves with a white section on the palms and black boots.

Personality
Unlike most other demons, Byakomaru seems to be very protective over Shinya, as he warned Mahiru to keep away from him, and grew agitated when the latter threatened to kill Shinya if he finds out what she's plotting.

However, he does not seem to care about other matters, shown when he told Mahiru that he doesn't really care who she is and what she is, as long as she does not harm Shinya.

Byakomaru seems to be more a wise demon and calm, having never asked Shinya for desires repeatedly who unlike most demons does, as he cares for Shinya's well being.

History
Byakomaru's past is mostly unknown, but judging by Byakomaru's red eyes and fangs,  he was once a vampire before somehow becoming a demon. At some point he got sealed inside a Cursed Gear, and later in the year 2012, became Shinya Hīragi's gear.

Events of 2012
Byakomaru was contracted with Shinya. According to the light novel, Shinya underwent an operation to increase his chances of handling a Black Demon Series Weapon, and he emerged from the operation successfully. Ever since then, Byakomaru became his primary weapon.

Events of 2020
Shinya uses Byakomaru in battle against the vampires.

Osaka Arc
In Chapter 54, he manifests to confront Mahiru Hīragi on the roof of a moving car. He demands to know what Mahiru is as he says that she is not a demon, and threatens her if she tries to harm Shinya. He reappears again in Chapter 56 to warn Shinya that Guren is trying to kill him; and when Shinya is getting ready to fight Guren, Byakomaru is confident in Shinya's chances of winning due to the advantage of distance, but is told to not always expect things to go as planned.

Shibuya Arc
The white tiger energy is fired at a Hyakuya agent during the attack on Shinjuku only to be deflected by the weapon form of Jigenso. Multiple forms are launched only to travel into Crowley when the agent opens a portal to achieve that end.

In the challenge to restrain Guren, Byakomaru is asked by Shinya to give him more power. Byakomaru does not, and appearing in a human like form, he advises Shinya that Guren is not wielding a normal demon. Shinya does not care, but Byakomaru says otherwise, explaining to him that it is how he always survived before, by staying aloof, and unattached from everything. Despite that, Byakomaru observes that Shinya still holds burning desires.

He is aware that when Shinya stole the lives of others just to survive, he feels nothing, even at the prospect of losing his own life. Tapping Shinya's chest and producing visualisations of the other children laying deceased around Shinya, Byakomaru raises the time when Shinya was bought to be Mahiru Hiragi's fiancé, when he was trained against other children in battles to the death, Shinya survived because he never lost his cool. In the landscape with Mahiru Hiragi remembered as a young girl watching him, Byakomaru stands untouched by the heavy rain watching a young Shinya and finishes that even though he never managed to make Mahiru his, he still feels nothing. He agrees with Shinya's assertion that there is no need to make an effort since a thing can be lost regardless. It is believing that way which fulfils Shinya's desires, this time is the same as any other and Byakomaru says that Guren is beyond saving. Advising him to run, he asks what makes Shinya so obsessed with him when he remains set on saving Guren.

With it assumed that as Shinya's demon, Byakomaru knows the reason, he answers that it comes down to Guren having what Shinya does not. Byakomaru voices that Guren lives in a world more soaked in despair and helplessness, than even Shinya. What is more, he was born in a family just for the Hiiragi's to ridicule him, saddled with a fate that he will never get anything no matter how hard he tries. Byakomaru says that he thought Shinya hated idiots when Shinya describes Guren as one for never giving up. He states that if Shinya allowed himself to be stupid even for a moment, he would not have survived. Acknowledging that Shinya hates idiots, Guren included, Byakomaru encourages that he abandon him. He knows that Shinya says he will abandon Guren, but in the end he will not. After a pause, Byakomaru says it is as if Shinya is in love.

Not swayed by Shinya's reasons to want to help, Byakomaru is certain that if Shinya tries to save Guren now, he will die, he does not have enough power. Calling Shinya wise, it is how he has survived. His persuasion raises that is Shinya let's himself be stupid, he will die and then asks if he intends to die here. Byakomaru would rather he did not, it would be a problem since he is his demon. Simply asking what when SHinya feels he would have one small regret if he died, Byakomaru is called upon to devour Shinya's desires. Closing his eyes, he complies with the request and instructs Shinya to give name to his desire.

Giving the power Shinya wants, Shinya is turned into a two horned demon from Byakomaru's power. The rifle is used to fire into Guren as a demon.

Forms and Abilities

 * Demon's Thrall: Byakomaru can enter it host's dreams and memories to create nightmares and break it's host's will. This is done in order to take over his body. This ability can only be used against his host.
 * Basic Form: Byakomaru takes the form of a black, green striped sniping rifle with a bayonet attached at the end . Byakomaru's specialty is long-range firing, and it is not very effective in close-range combat.
 * Multiple White Tigers: Shinya can fire bullets which splits and then manifests into several tigers. Each tiger can strike its target independently.
 * Hidden Bullet: Shinya can fire a bullet which appears behind his target, as shown when fighting with Yūichirō Hyakuya in chapter 17, "Cursed Guinea Pig." It is shown to be an effective surprise attack, but Shinya revealed to Yu that he can only activate that ability once for an unspecified amount of time.

Shinya Hīragi
Byakomaru is Shinya's cursed gear. He is protective of Shinya as seen when he threatens Mahiru he will do something if she hurts him. And also when Guren knocked everyone out except for Shinya; he tells Shinya that Guren is not to be trusted any longer because it could put Shinya in danger. Byakomaru works close enough with Shinya to target specific enemies. He initially refused to give Shinya power and encouraged him to flee when they were against an especially dangerous foe. Trying to remind Shinya that he has survived by staying detached from everything, Byakomaru taps into Shinya's past experiences to encourage him to stay aloof to Guren being transformed into a demon.

However upon Shinya revealing his only true desire to never give up on his friend and realizing that there was no talking him out of helping Guren, Byakomaru eventually conceited to Shinya's demand for more power and boosted his abilities and powers to the point that like Guren and Yu, Shinya has now willingly allowed himself to become a Demon.

Mahiru Hīragi
Byakomaru meets her for the first time when Guren Squad goes to Osaka. He is cautious of Mahiru because he can tell she is not a demon but chooses to do nothing about it.

When he is trying to have Shinya leave Guren behind, Byakomaru has a memory like illusion of the young girl appear overlooking Shinya's training, and points out Shinya never anything when he failed to make Mahiru his.

Guren Ichinose
Byakomaru warns Shinya that Guren is trying to kill him; and when Shinya is getting ready to fight Guren, Byakomaru is confident in Shinya's chances of winning due to the advantage of distance, but is told to not always expect things to go as planned.

To preserve the life of Shinya, Byakomaru speaks in depth to persuade Shinya to abandon Guren. He comments on the state of Guren's life and uses that knowledge to attempt to diminish Shinya's perceived obsession with him.However during the course of their conversation inside Shinya's Mind, Byakomaru eventually realizes that Shinya's only true desire is to help and save Guren,causing him to then give up on trying to convince his master to save himself and conceded to grant him more power to the point that Shinya himself has now become a Demon due to being further empowered.

Quotes

 * "What are you? You are no demon."--To Mahiru Hiragi, Chapter 54, "Sinner's Christmas"
 * "But if you even think of harming Shinya--"--To Mahiru Hiragi, Chapter 54, "Sinner's Christmas"
 * "Shinya. You must not trust him anymore. He will kill you."--To Shinya Hiragi, Chapter 56, "Loose-Lipped Vampire"
 * "No, Shinya. I will give no more."--Providing more power will do no good with it not being a normal demon they are against, Chapter 83, "Two Demons, page 7"
 * "When you were bought to be a mate for Mahiru Hiragi... ...and when you were trained against other children in battles to the death... ... you survived because you never lost your cool."--Vividly aware of Shinya's past, whilst placing a young Shinya in a visualization of the events, and attempting to dissuade Shinya from fighting, Chapter 83, "Two Demons, page 10"
 * "He lives in a world more soaked in despair and helplessness than even you. Born into a family which exists solely so that it can be derided by the Hiragi family. Saddled with a fate which decrees he shall never acquire anything, no matter how he tries."--His expressed view on Guren, after wondering why Shinya would be obsessed with him after assuming it is because he has what Shinya does not, Chapter 83, "Two Demons, page 13"

Trivia

 * In the fanbook, it is revealed that the tigers are fired from the rifle. Shinya fires a single bullet, which then manifests into Byakomaru's tiger form.