As someone who has read almost all of your stories!! (1/2, i have a lotttt to say)
1. Check out maziikkin (i think thats how u spell it, if not I'll come back later) and dvtoyevsky. I am 100 percent sure ur gona love their writing styles. anddd they have fyodor stuff. and dazai. and nikolai. and chuuya, and akutagawa, and, and...
2. I forgor
3. Fyodor is not dead okay? He. Is. Not. Dead. Here's a reddit theory.
1.Fyodor has been around for 4 seasons. Why would Asagiri waste all of this buildup and not give him a backstory or more character depth? we don't even know what his ability is. Asagiri made such a big deal out of it, just to kill him off? That makes no sense storytelling wise.
2. Fyodor's ability could be his trump card. As mentioned above, we never found out. Instead, he died abruptly without ANY kind of explanation about it.
A thought I had was that Fyodor's ability could be what caused those last few minutes of episode 11– the ones where Atsushi and Akutagawa fight against Fukichi, who's mask looks JUST like the one in the new volume 24 DOA official art. Why would the other members of the Decay get their own designs and art for this? Probably because they're gonna make an appearance too. Which would mean Fyodor, as well as Sigma, would come back.
3. While receiving information about Fyodor, Sigma asked "What are you?". Fyodor might not be human. I mean, Lovecraft exists, it's not out of question. And BSD has a big thing going on with people not feeling human. Fyodor is known as a "demon". He possesses extreme intelligence and huge manipulation skills for unknown reasons, is SUPER evil, has a sickly body but still manages to stay just fine— While this is all doable for a human in the BSD world, it's still possible that he isn't. Maybe he's immortal, or doesn't die easily.