Fyodor Dostoyevsky

Fyodor is a tall and slim young man, with a bit of an anemic constitution. He is described to have a thin, pale face and long messy hair of a purplish black, somewhat disheveled, that reaches his shoulders. His most noticeable facial features are his sharp, dark red-purple eyes with light bags underneath, giving them a tired look. His attire is formal. He wears what appears to be a long-sleeved buttoned white shirt, with light purple cuffs and outlines, and white pants. It is accompanied by a long black coat with a few yellow buttons, reaching Fyodor’s knees, along with a white fur collar. He also wears a white ushanka hat, and long boots of a dark maroon color.

Although he's a very enigmatic individual, Fyodor is a man who is known for his cunning, unpredictable and sinister nature. He is composed and confident, and even in dire situations, he hardly falters and doesn’t appear to fear his enemies, conjuring conniving plans and strategies that result in his success. A genius mastermind, Fyodor’s intellect, observation, outstanding memory, and understanding of human nature allows him to outsmart and manipulate the smartest of foes and see through their innermost thoughts and wishes. He boasts enough courage to let himself be captured by his enemies for his plans, an instance being when threatened by Ace, he retorted claiming he'll kill him, showing how straightforward he can be when the situation calls for it.

Fyodor's most noticeable characteristic is his religiousness, viewing himself as a "servant of God" and how he views salvation, saying things like "A blessing for children." and how God wishes for perfection and harmony over anything else, all while committing immensely cruel and unforgivable acts of evil. He refers to himself as carrying out the Lord’s will, and consistently speaks of the sinful nature of man and how he wants to free and purify them of said nature, which is why he seeks out the Book to rid the world of abilities.

When it comes to his lackeys from the Rats in the House of the Dead and his allies from the Decay of the Angel, Fyodor views them as pawns he uses to help him achieve his goals and cast them aside, if not dispose of them later on. He neglected Nathaniel Hawthorne's wish to save Margaret Mitchell by brainwashing him and erasing his memories of everything other than her, exploiting the former's desire to save her for his own benefits. When Sigma finished playing his role at the Sky Casino, he betrayed him out of nowhere by attempting to assassinate him. Dazai even states that Fyodor would have killed Sigma if he hadn't chosen him to be his helper during the prison break.

Befitting of his title, "Demon", Fyodor is also shown numerous times to put the lives of innocent people in danger to get what he wants. He was heartless enough to psychologically manipulate a young girl into blowing herself up to "save her brother" when in reality, he convinced her to do it just to crush Kunikida's spirit and prevent his further interference in Fyodor's schemes. While the Agency and the Mafia were hunting Fyodor down, he held a passersby hostage using live grenades, and after coercing another Ability user into helping him, he ruthlessly killed her, despite her aiding him and her pleas for him to spare her life.

Despite his cruelty and lack of remorse, Fyodor speaks in a polite and discreet manner, and is occasionally amicable around others. He seems to have refined tastes, as he enjoys playing the cello and listening to classical music. Although he is generally uncaring of others on a personal level, he is capable of feeling love and showing affection in his own way if he wishes—it has been stated he has a genuine love for humanity, is attracted to those who "have a good or healthy complexion", and would "gift land or a country" to someone he loves.