Asuramaru is a striking and androgynous figure, characterized by his long, dark purple hair that cascades beyond his feet. His bangs cover his left eye, and his hair flows gently in the breeze when within his own realm. When he walks in the physical world, his hair is parted into two sections at the back. As a vampire-turned-demon, Asuramaru’s appearance is marked by red eyes, fangs, and pointed ears. His transformation into a demon is further reflected when his horns grow larger and his nails become sharp claws as the curse restraint loosens.

As for his attire, Asuramaru wears a sleeveless, open-back dress adorned with a collar of gold beads that cover his throat. The chest piece is black, while the rest of the gown is white, with slits at his outer thighs, allowing him full movement. He wears black sleeves that reach from mid-upper arms to his middle fingers, with each sleeve attached to a ring. Asuramaru is barefoot, further emphasizing his ethereal and otherworldly nature. He completes his look with a headband formed of two parallel golden strips that match the horns piercing through his hair near his hairline.

Asuramaru also has the ability to take on different forms, being a mental construct tied to Yu’s memories. He can appear as various figures from Yu’s past, such as a 12-year-old Mika, Akane Hyakuya, or other Hyakuya orphans. He uses these forms strategically, often to manipulate Yu and break his will by weaving them into memories, including those with Yu’s parents. His shifting appearance is a powerful tool in his ability to influence and control Yu.

Asuramaru is an emotion-driven and bloodthirsty demon who thrives on consuming Yu’s blood. He often displays haughty arrogance, boasting about his superior power and how easily he could crush Yu if he desired. Like many demons, Asuramaru is manipulative, using nightmares and traumatic visions to break his host’s spirit and take control of his body. Each night, he disturbs Yu’s dreams with visions of Mika asking why Yu left them to die, further torturing his host emotionally and psychologically.

When possessing Yu, Asuramaru treats it like a game, playing out moves such as inducing nightmares and biting Yu’s neck, seeing them as mere tactics to achieve his goal. He becomes irritable when things don’t go according to his plans, particularly when Yu defies his ‘rules’—such as throwing a sword in front of him while dashing to attack. Asuramaru relishes the chaos of their existence, especially when vampire nobles make their presence felt, but he remains largely indifferent to them, viewing their threats as minor nuisances compared to his own ambitions. He enjoys the trouble that Yu’s actions may bring, furthering his desire to push Yu into situations that might grant him more power.

Asuramaru holds a deep disdain for humans, viewing them as vile, greedy creatures even worse than vampires or demons. Despite his superiority complex, he looks down on weaker demons, but is entirely indifferent to other powerful beings like vampire nobles, even when Yu’s life is at risk. To him, the presence of these beings is a source of detachment, rather than fear or concern. His primary focus remains on encouraging Yu to grow stronger, with the intention of eventually fully possessing his body. When it comes to seraphs, Asuramaru is aware of their power and views them as potentially more dangerous than demons, even considering Yu’s acceptance of a seraph trumpet as a betrayal.

Though Asuramaru is clearly a trusted enemy rather than an ally, he does occasionally provide Yu with useful information, such as revealing Yu’s non-human traits. He recognizes some of Yu’s better qualities but often does so without any personal gain, further underlining his detached, calculating nature. Despite the torment he inflicts on Yu, Asuramaru is keen on guiding him toward greater power, seeing their relationship as one of mutual benefit—though his motives remain far from benevolent.

Asuramaru was bound as a Black Demon to a katana, residing within the weapon for a significant period of time. He was kept hidden in the depths of Second Shibuya High School, within a room themed around demons. This room was adorned with traditional depictions of demons in statue form, adding to the eerie atmosphere in which Asuramaru was contained. His existence within the sword was one of waiting, prepared for the moment when he could be unleashed, with the potential to take over a host. Eventually, Yu Ichinose would come into contact with the weapon, unwittingly releasing Asuramaru and forging the contract that would bind their fates together.

Possession and Manipulation
As a possession-type demon, Asuramaru specializes in infiltrating and taking over his wielder’s body. His ability to appear as figures from Yu’s life, such as Mikaela, enhances his manipulative tactics.

Enhanced Combat Power
Through the Black Demon Series Cursed Gear, Asuramaru enhances Yu’s physical abilities, granting him superhuman speed, strength, and agility in battle.

Specialized Knowledge
Asuramaru possesses extensive knowledge of curses, demons, and their weaknesses. His insights have been critical in helping Yu navigate difficult situations and utilize his power effectively.

Yūichirō Hyakuya
Asuramaru’s wielder and target for possession, Yu is both a source of frustration and fascination for the demon. Their dynamic is one of constant struggle, with Asuramaru testing Yu’s resolve while providing him with the power he needs to survive.

Mikaela Hyakuya
Asuramaru often takes Mikaela’s form to manipulate Yu. This tactic highlights the demon’s understanding of Yu’s psyche and his reliance on emotional manipulation.

Other Black Demon Series Demons
Asuramaru is one of the high-ranked possession-type demons in the Black Demon Series, reflecting his strength and status within the hierarchy of cursed entities.

Asuramaru plays a pivotal role in Seraph of the End, representing the duality of power and danger inherent in the Cursed Gear. His manipulative yet invaluable contributions to Yu’s battles highlight the complexity of their relationship, adding layers of tension and intrigue to the story. As both an ally and a potential adversary, Asuramaru’s presence underscores the series’ themes of strength, sacrifice, and inner conflict.