Bungou Stray Dogs follows the Armed Detective Agency, a group of "gifted" people who use their talents to solve crimes and protect Yokohama from the various gangs that roam the streets. Unfortunately, the most recent episode of Season 4 reveals that the agency is currently in hot water due to circumstances beyond its control. They were duped into believing they were rescuing hostages, only to turn out to be the perpetrators in the blink of an eye. They switched places with the perpetrators so quickly that the agency members couldn't process what had happened.
This was due to the Book, a supernatural object that transforms whatever is written inside into truth. The Decay of Angels is a terrorist organization that stole a page from the Book, and its members intend to run a smear campaign against the Armed Detective Agency in order to undermine public trust in their work. However, each member appears to be seeking the Book for a different reason. Fyodor Dostoevsky has long been a thorn in Yokohama's side. Fyodor is an enigma in Bungou Stray Dogs, with a dangerous ability that allows him to kill someone with a single touch and an eerily calm demeanor at all times. However, his reason for wanting to get his hands on the Book is perhaps the most compelling.
Why is Fyodor Interested in the Book?
The Book is a mysterious supernatural object. Taneda proposed that the Book is an extension of an ability user's power, though Ranpo deduced that it's something far beyond the average "gifted"'s abilities. As the leader of the Rats in the House of the Dead, Fyodor has taken a particular interest in hunting the Book down, in order to get rid of all the ability users in Yokohama. He took advantage of Alexander's ability, A Feast in Time of Plague, to start an endemic with a poisonous virus that would put members of the Port Mafia and Agency out of commission so locating the Book would be easier.
Fyodor claims that he wants the Book to cleanse humanity of its "sins." In this case, Fyodor sees all abilities as sins that must be cleansed from the world. His own ability is quite brutal, and he doesn't seem to mind using other people's powers for his own ends; he simply wants to get rid of them all. He sees the abilities as "sins," so every user, including himself, is a sinner.
Why Does Fyodor Want to Get Rid of Every Power?
Fyodor is clearly not a cold-hearted murderer like many anime villains throughout Bungou Stray Dogs. On the contrary, he appears to regard murder as a necessary evil in order to achieve his ultimate goal. It's heavily implied that Fyodor is uncomfortable killing others on some level. This creates an interesting moral quandary for Fyodor because his ability demonstrates the fragility of human life. Fyodor's Crime and Punishment grants him the ability to kill someone with a single touch.
The name "Crime and Punishment" also implies that everything Fyodor does is a crime, so the ability is an eternal punishment in and of itself. Fyodor describes abilities as "sins" and users as "sinners." Not much is known about the capabilities of Fyodor's ability at this point -- whether his killing ability is controllable or not remains unknown for now. However, since he's so passionate about getting rid of abilities, believing the latter isn't too big a stretch. He's not putting himself on a hypocritical pedestal to ensure he'd be the only ability user in Yokohama. On the contrary, Fyodor may view himself as a sinner on the same level as his enemies. By eliminating everyone's abilities, including his own, he'd be free of the "punishment" to which the ability has subjected him.