Fyodor is the leader of an underground organization called the Rats in the House of the Dead and is the founder and former member of the Decay of the Angel. His goal is to find the reality altering book that's hidden deep within Yokohama to use it and rid the world of all its ability users.
Because of his very high level of intellect, Fyodor is one of the most difficult opponents the Armed Detective Agency has ever faced. He serves as both the acquaintance and archenemy of Osamu Dazai. 