Fyodor Dostoevsky, often referred to as Fyodor D, is a primary antagonist known as the leader of the terrorist organization the Rats in the House of the Dead and a key member of the Decay of the Angel. He is a tall, slim young man with long, dark, messy hair and sharp dark eyes that often give him a tired appearance. His typical attire consists of a white shirt and pants, a long deep red coat with white fur, and an ushanka hat, complemented by red long boots.

Fyodor presents a calm and confident demeanor, rarely showing fear and possessing enough nerve to willingly allow himself to be captured by enemies as part of his schemes. He displays a sinister personality and immense arrogance, viewing himself as a god and speaking frequently about the sinful and stupid nature of humanity. He possesses a strong religious belief, seeing it as his divine mission to cleanse the world of sinners, a role he believes only he can fulfill. Despite this grand self-image, his primary nemesis, Osamu Dazai of the Armed Detective Agency, refers to him as a demon, noting a past encounter between them.

Fyodor’s ultimate motivation is to obtain a mythical and all-powerful artifact known as the Book. The Book is described as a single volume of blank pages onto which anything written becomes a tangible truth. He aims to use the Book to rid the world of all ability users, whom he considers the ultimate sinners. To achieve this, his overarching strategy involves first destroying the two most powerful ability-user organizations in Yokohama: the Port Mafia and the Armed Detective Agency.

As a criminal mastermind, Fyodor relies on intricate manipulation rather than brute force. He often sets elaborate traps that force his enemies to destroy themselves. For instance, he orchestrated a scheme called the Cannibalism strategy, using a virus-type ability to poison the leaders of both the Agency and the Mafia, knowing the two organizations would be compelled to fight each other to save their own leader. He also famously engineered his own capture by a Port Mafia executive named Ace. While imprisoned, Fyodor psychologically manipulated Ace into committing suicide, solely by leading him to believe he had uncovered the secret of Fyodor's non-existent ability. Afterward, he killed a young subordinate, Karma, without hesitation to eliminate a witness, demonstrating his ruthless willingness to sacrifice anyone. His key allies and subordinates include Nikolai Gogol and Sigma of the Decay of the Angel, as well as Nathaniel Hawthorne, whom he manipulated by offering to heal a loved one.

The most significant relationship in Fyodor’s story is his rivalry with Osamu Dazai. Their encounters are depicted as a battle of wits between two nearly equal intellectual giants. Dazai is the only person who consistently anticipates Fyodor’s moves, and Fyodor, in turn, sees a dark reflection of himself in Dazai, at one point asking if they are alike. Their conflict culminates in a psychological duel within the high-security prison Meursault, where both are eventually detained.

Fyodor’s ability is named Crime and Punishment. The exact mechanics of his power remain ambiguous, but its primary known effect is the ability to kill any person instantly with a single touch. This lethal effect is not limited to skin-to-skin contact, as he has killed a government agent through his gloves. During an incident involving a mist that separated ability users from their powers, Fyodor's ability did not leave him. Instead, it manifested as a separate entity, declaring itself to be the punishment for Fyodor’s crime, implying a deep, symbiotic connection between the user and his power. Throughout the series, Fyodor does not experience a typical redemption or emotional development; he remains a static and unwavering antagonist, relentlessly pursuing his goal of erasing ability users from the world.