Fyodor Dostoevsky, dubbed "Demon Fyodor," emerges as a central antagonist driven by a rigid ideology fixated on eliminating supernatural ability users, whom he deems inherently corruptive to humanity. As founder of the Rats in the House of the Dead and a pivotal force within the Decay of the Angel, he seeks a reality-altering book to purge these abilities, framing his crusade as a divine mission. He rationalizes acts of terrorism and manipulation as sacred steps toward global purification, cloaking his violence in rhetoric of salvation. Pale and slender, his striking purple eyes and tousled purplish-black hair contrast with a wardrobe of white shirts, black fur-lined coats, and a white ushanka. After usurping Bram Stoker’s body via his ability, his appearance shifts to match the vampire’s gothic aesthetic. His power, *Crime and Punishment*, enables consciousness transfer into the body of whoever kills him, perpetuating his identity across lifetimes. This ability grants near-immortality, evidenced when Sigma’s memory probe reveals endless layers of his existence. Spanning centuries, his history includes capture and execution by Bram Stoker’s forces, only to hijack his executioner’s form. He later manipulates Ōchi Fukuchi, leader of the Hunting Dogs, by forging a prophecy of impending war, spurring Fukuchi to establish the Decay of the Angel and incite global terror. Alliances with groups like the Guild and Order of the Clock Tower underscore his tactical exploitation of external factions, though he discards allies like Sigma after leveraging their roles in schemes such as the Sky Casino. Merging cold logic with feigned humility, he poses as a devout servant of higher purpose while orchestrating carnage. Human suffering amuses him; he treats conflicts as intellectual games, exemplified by his collaboration with Shibusawa during the Dead Apple incident to trigger worldwide chaos for mere entertainment. Despite professing peace, he employs ruthless tactics—pushing a child to suicide to destabilize Kunikida or deploying civilians as pawns. Notable schemes include framing the Armed Detective Agency for terrorism, sparking ability-user wars via a viral pathogen, and infiltrating Meursault prison through staged imprisonment. Though a helicopter crash severs his arm, he survives by transferring into Bram Stoker’s body, perpetuating his influence. His rivalry with Osamu Dazai hinges on their mutual recognition as cunning equals, each navigating moral grayness. Emotionally detached, he wields rhetoric and symbolic gestures—open hands mimicking vulnerability, dialogues blending blessings with nihilism. Self-described frailties like anemia juxtapose his mental fortitude, blurring lines between fragility and menace. His origins remain shrouded beyond ties to literary history, while his legacy cements him as a paradox: a harbinger of chaos masquerading as a utopian visionary, seeking purity through annihilation.