Alma is a complex figure introduced in D.Gray-man Hallow, whose existence is intrinsically tied to the tragic history of the Black Order and its forbidden experiments. He is a young man with a slender build and east Asian features, originally created as part of the Second Exorcist Program, also known as the Second Apostle Project, which aimed to produce artificial exorcists with enhanced regenerative capabilities. Within this program, Alma was a unique success, a living being whose body was built around the preserved brain of a deceased exorcist. This origin places him at the center of the Order's darkest secrets, as his very existence blurs the line between human life and disposable military asset. His physical appearance is marked by the trauma he has endured; as a child, he had short, unruly dark hair, but after being severely injured and subsequently kept in a state of suspended animation for years, his body became covered in scars and restrictive tattoos. Upon transforming into a demon, his features become more grotesque and inhuman, reflecting his corrupted state.

At his core, Alma's personality is defined by a profound and tragic loneliness. Before awakening his fellow test subject, Kanda Yu, Alma spent his early conscious days alone, developing a habit of talking to the other still-sleeping Second Exorcists in their pods, memorizing their names and telling them about his day in the hope they would wake up and be his friends. He is naturally cheerful, optimistic, and unusually resilient, maintaining a bright and almost naively curious demeanor despite the constant pain of synchronization experiments and the sterile, oppressive environment of the laboratory. This initial personality is characterized by a childish enthusiasm for mundane things, a desperate eagerness to connect with others, and a stubborn refusal to give in to despair. However, this cheerfulness masks a deep well of pain. When pushed too far, he is prone to emotional outbursts and tears, but he never uses his suffering as an excuse for self-pity. His primary motivation in his early life is simple: to make a single friend. He latches onto Kanda with fierce loyalty, determined to break through the other boy's hostile exterior.

Alma's role in the story is that of a catalyst, a living embodiment of the Black Order's sins who serves as the central figure in a tragedy that forces several characters to confront their pasts. He is directly responsible for two major catastrophic events within the Order. The first occurs nine years before the main events of Hallow, when Alma, having regained the traumatic memories of his past life, goes on a rampage. He massacres the staff of the Asian Branch laboratory and attempts to kill Kanda, leading to his own death at Kanda's hands. The second event takes place in the present, after his mutilated body has been secretly repurposed by the Order as the living womb for the Third Exorcist Program. When the Noah family intervenes and restores his consciousness by flooding him with Kanda's memories, Alma awakens as a powerful, vengeful demon and destroys the North American Branch, setting the stage for a final, agonizing confrontation with Kanda.

The central relationship in Alma's existence is with Kanda Yu. Their bond is a tangle of friendship, violence, and a shared identity as artificial beings. Initially, Kanda found Alma's clingy, cheerful personality annoying, and their interactions frequently devolved into physical fights. However, over time, they became each other's only confidant, two lonely souls trapped in a nightmare. Alma's greatest act of friendship was helping Kanda escape execution, an act that triggered his own fatal breakdown. The tragedy deepens with the revelation of Alma's true nature: the brain within his artificial body once belonged to a female exorcist who was the lover of Kanda's own previous incarnation. This means the person Kanda has been searching for his entire life, the woman whose memory haunts him, is, in a sense, Alma himself. This knowledge is what drives Alma to madness; he attempts to kill both himself and Kanda not out of simple malice, but out of a desperate desire to prevent Kanda from ever learning the terrible truth and to free them both from their cursed existence.

Alma's development is a heartbreaking arc of loss of self. He begins as an innocent, hopeful child and transforms into a creature of pure anguish and destruction. His final moments, however, offer a semblance of peace. Through the intervention of Allen Walker, Kanda learns the truth and, instead of rejecting Alma, accepts him completely, calling him a fool and holding him as he dies. In his final moments, Alma's soul is seen taking the form of the female exorcist she once was, walking hand-in-hand with the childlike incarnation of his pain into the afterlife, finally free from the cycle of death and rebirth imposed upon him by the Order.

In terms of abilities, Alma is an extraordinarily powerful combatant. As a Second Exorcist, he possesses a seal on his chest that grants him phenomenal regenerative powers, allowing him to reattach limbs or even resurrect from fatal wounds, though repeated use weakens his body. His physical strength and speed are far beyond a normal human's, capable of besting multiple armed adults even as a child. After being transformed into a demon, he gains a host of new, terrifying powers. He can fire concentrated beams of destructive dark matter from his hands and mouth, generate an electric field to paralyze opponents using eyes that form in his palms, fire long spikes from his mouth, and extend his tail to ensnare targets. Like all demons, he also possesses a self-destruct mechanism, which he attempts to use to kill himself and Kanda in a final, devastating explosion. Furthermore, Alma is capable of synchronizing with a parasitic type of Innocence that manifests as long, sweeping blades from his right arm, a weapon that originally belonged to his female past life. This combination of holy weapon and demonic power makes him a uniquely tragic and dangerous force, a living contradiction whose very body is a battlefield for the war between Innocence and Dark Matter.