Fyodor Dostoyevsky is a tall, slim young man with long, dark, messy hair that reaches his shoulders and sharp, dark purple eyes that often give him a tired, distant look. He typically dresses in a white buttoned shirt and white pants, paired with a long black coat trimmed with white fur, an ushanka, and red long boots. In the film Bungo Stray Dogs: Dead Apple, he appears as a mysterious and calm figure who moves through the shadows of Yokohama with a quiet, confident demeanor, showing no fear of his enemies and even allowing himself to be captured when it suits his plans. He is a person of extreme intelligence and a truly sinister personality, marked by arrogance and a strong sense of his own purpose. He speaks frequently about the sinful nature of humanity and seems to view himself as an agent of divine will, a conviction that leads him to call himself a god, while his rival, Osamu Dazai, refers to him as a demon.

In Dead Apple, Fyodor acts as a shadowy manipulator behind the chaos created by Tatsuhiko Shibusawa, a man known as the Collector. Six years prior to the main events of the film, Fyodor observed the bloody Dragon's Head Dispute from a distance, finding it entertaining. In the present day, he works with Shibusawa to enact a plan that covers Yokohama in a strange fog causing Ability users worldwide to commit suicide using their own powers. Fyodor provides Shibusawa with information and resources, helping him collect Abilities in the form of glowing red crystals and ultimately aiding him in unlocking his full power and lost memories. Fyodor's own Ability, named Crime and Punishment, is noted to remain intact and unaffected by the lethal fog, which he explains is because crime and punishment are close acquaintances. He describes the resulting chaos as the incarnation of the combined turmoil of all Abilities. Although he appears to be an ally to Shibusawa, his loyalty is fleeting, and he is ultimately using the situation for his own ends. When the plan reaches its climax, Fyodor is seen watching the final confrontation, and after Shibusawa is defeated, he calmly walks away, mentioning his need to locate a certain book, the same reality-altering artifact that is his true goal.

His key relationships in the film are defined by manipulation and rivalry. He works alongside Shibusawa, but with clear duplicity, as his primary interest is not in Shibusawa’s success but in the chaos and data the conflict generates. He also shares a complicated past with Osamu Dazai, having apparently worked with him in some capacity years ago. Dazai is seemingly the only person who can truly anticipate Fyodor’s moves, and their interactions are filled with a mutual recognition of each other as dangerous, intelligent, and kindred spirits. Fyodor is also watched by the government's Special Abilities Division, which is aware of his dangerous nature but struggles to contain or understand his motives.

Throughout Dead Apple, Fyodor does not undergo significant personal development, instead remaining a static and enigmatic force. His smug contentment and sense of amusement as the events unfold suggest that the entire incident is less a grand scheme and more a form of entertainment for him. His motivation is deeply rooted in his philosophy that death is salvation and that Ability users are sinners who must be punished and cleansed from the world. He desires to obtain a mythical book that can rewrite reality, which he would use to rid the world of all superhuman Abilities, an ironic goal given his own status as a powerful Ability user. He has a habit of biting his thumbs until they bleed and is noted to have a weak, anemic constitution, a physical frailty that contrasts with his immense psychological and tactical power. His portrayal in Dead Apple solidifies him as a patient, god-like mastermind who views the world as a game board and the people on it as pieces to be manipulated in pursuit of a twisted form of salvation.