Fyodor Dostoevsky is a tall, pale man with sharp dark purple eyes and shoulder-length purplish-black hair, often appearing disheveled. He typically wears formal attire: a white shirt with light purple accents, white pants, a long black coat featuring a fur collar and yellow buttons, maroon boots, and a white ushanka hat. While imprisoned, he wears standard white prison garb. He leads the underground organization Rats in the House of the Dead and founded the Decay of the Angel. His primary objective is to acquire a reality-altering book to eradicate all ability users globally, viewing their powers as inherently sinful and requiring purification through death, which he equates with salvation. He paradoxically pursues this goal despite being an ability user himself. His ability, *Crime and Punishment*, allows him to possess the body of anyone who kills him, transferring his consciousness and appearance to the perpetrator. This ability remains loyal to him, declaring itself the "punishment" to his "crime" during external threats like Shibusawa's mist. It also grants him an extended lifespan, as glimpsed by Sigma. Fyodor exhibits a calm, calculating demeanor, displaying exceptional strategic intellect, photographic memory, and a profound understanding of human psychology. He manipulates individuals and organizations by exploiting their desires, such as deceiving Fukuchi Ōchi with a fabricated prophecy of a future world war to instigate global terrorism via the Decay of the Angel. He views allies like Nathaniel Hawthorne and Sigma as expendable pawns, discarding or betraying them once their roles conclude—exemplified by orchestrating Sigma's assassination after the Sky Casino operation. He frames his actions as executing divine will, frequently referencing God's desire for "perfection and harmony" while committing mass murder and terrorism. He rationalizes atrocities like manipulating a child into suicide or enabling Bram Stoker's vampire outbreak as necessary for humanity's salvation. This dichotomy earns him epithets like "Demon" from adversaries such as Osamu Dazai, who notes Fyodor only trusts those he can manipulate and lacks genuine allies. Fyodor's background includes early manipulation of key figures: he took over Bram Stoker's body after being killed by Bram's executioner, allied with the Guild to locate the book, and met Sigma three years prior to the main events, offering him a "home" in exchange for service. His schemes include the Moby Dick crash in Yokohama to eliminate ability users, the Cannibalism incident to pit the Armed Detective Agency against the Port Mafia, and the Sky Casino and Meursault prison arcs to advance his goals. Philosophically, he perceives death as liberation from human suffering and sin, stating humans "cannot help but kill each other" and require external purification. This aligns with his self-proclaimed role as an agent of divine punishment, though his occasional expressions of sorrow—such as when killing Karma—hint at inner conflict. His dialogue often incorporates religious terminology, like blessing "children" or desiring "peace to all the world," contrasting with his violent methods. After being captured and imprisoned in Meursault, Fyodor continues influencing events, including orchestrating a prison break with Dazai and Sigma. His ultimate fate remains unresolved, but his actions consistently position him as a catalyst for conflict, driven by an enigmatic desire to fulfill what he interprets as a predestined role as the narrative's necessary antagonist.