essentially what we found out in ch 113 and 114 is:

• fyodors fucking ancient as old as the dinasours atp (jk since 1400/1500ish from what we can see from the manga)
• sigma reading fyodors memories

following MY own theory about fyodor (before 114 came out) 
i have 2 theories. the asagiri skinned fyodor theory and the fyodor created the book/the book created fyodor theory

both theories combined no particular order because i just yap and the theories inside the two theories flow/connected/arevthe same anyways the outcome is just slightly different.
essentially the asagiri skinned fyodor theory is that fyodor is the book itself. His ability IS THE BOOK. im only saying asagiri skinned fyodor bc asagiri is the author and did you know that people have used human flesh/skin/bones to make the cover of real books? yeah thats where the skinned fyodor comes from. ngl i kinda wish fyodor was skinned. that ugly af rat has been introduced since like THE BEGINNING of bugou gay dogs. like bro we get it. ur arc is over. just die and stay dead please . aaand i rambled on... BUT YEAH. Fyodor BEING the book itself/ his ability IS the book would probably not make sense im yapping on about something stupid and going insane. the other question is that who is sigma and bc sigma was born JUST THREE YEARS AGO. who tf wrote him into the storyline using THE BOOK???? YEAHHH ??? GET WHERE IM GOING???? I have like a massive big hunch that fyodor deliberately wrote sigma into the book. knowing that fyodor deliberately let sigma read his memories (dazai has speculated that sigma allowed him to read his (fyodor) memories in order to hide fyodor's ability since it isnt stated what his ability actually is. Either fyodor is the book itself or that he wrote the book/the book wrote him. If he wrote himself into the book that would kind of make sense since in 113 we see him kinda like about to get crucified or smth (croomfcification ig ) and knowing he would die back in the brams era (1400-1500/1600(?)) he wrote himself into the book prior as well as basically the whole like current timeline arc ig (doesnt make sense but lets run with it LMAO). and in 114 we see him get impaled by a fucking spear (LOLL what a fucking loser he shouldve been burned ngl..) we probably died with the book on him, the guards or some shit buried him and he's been like fossilled down deep in the earth. small detail to note, i recently watched perfect crime arc again (s4) and the book was mentioned. on the cover of the book it says stray dogs. you know who also says stray dogs? Dark era dazai, oda and ango in lupin bar. What if the earth shifted or smth and like his fossils ended under lupin bar or the ada (bc stray dogs,, dazai.. yknow RUN WITH IT IDK) and like the reason why FYODOR STILL HASNT FOUND THE FUCKING BOOK WHAT A LOSER is because when he wrote himself into the book he wrote that he would 'forget' about any connections he had with the book and he would search for the book. hence his appearance in yokohama. btw bsd is set in 2015 yokohama (they're still using flipphones ?? what) which means sigma was written into the timeline in 2012. sigma was born JUST 3 years ago. you know who else has the three thingo?? FYODOR.  this fucking rat istg. in the last ep of S5, fyodor gets impaled by a pole (how familiar,, as if he wasnt impaled by a spear back them cough cough) then the helicopter when helicopter helicopter, crashed into the tower (theres this 911 joke about it save me ) ANYWAYS. when the helicopter crashes onto the floor of the building (like the helicopter pad or some shit) he says the same words as jesus did before he was crucified, 'Eli, Eli, lama Sabachthani?' which is 'My God, My God, why have you forsaken me?' so kinda hinting that he's gona fucking ressurect or some shit (YEAH AS IF CHAPTER 114 ISNT CALLED RESSURECTION WHAT THE ACTUAL FUCK ASAGIRI ?!?!?!??!) also jesus resurrected 3 days later... SIGMA WAS BORN THREE YEARS AGO. CAN YOU SEE WHERE IM GOING WITH THIS SHIT. LIKE YA'LL CANT BE JOKING WITH ME WHEN SIGMA AND FYODOR ARE NOT FUCKING RELATED..

also side note, when i said that theres a chance someone wrote fyodor in the book (meaning that they also wrote sigma in,...) that person people are speculating is Leo Tolstoy i am going to run with that and say yes if fyo and sig were written into the book, tolstoy wrote them into the book/created the book. would kinda make sense since one of tolstoy's books is called resurrection AND YOU KNOW WICH CHAPTER WAS CALLED RESSURECTION /!?!?!? CHAPTER ONE HUNDRED AND FUCKING FOUR. ya'll cannot be shitting me with this. also other note is that recent theories were saying that fyo's ability is the transfer his death into those who killed him via contact with his own blood. this theory is MUCH valid than my crack book theory (since mine is outdated and it was yapping half the time, let me be delulu pls LMAO), this would kind of explain how fyo has been able to live and stay alive since jurassic park or someshit. bro probably experienced the ice age first hand ngl... maybe he caused the french revolution actually... he probably has been a terrorist in every era tbh (in the bsd timeline(s) ofc). the theory was linked to how kyouka's parents died (blood splattered onto them, causing them to do things without their will (killing themselves). which kind of makes sense a bit since in 114 we see a similar thing with the guard that impaled fyo where the blood ended up on the guards eye and at a side profile shot you could see veins sticking out.  yeah thats pretty much it with the theory ,, honestly i think this would be the most likely outcome since this is like the most trustable/ liable am i using the right words?? yeahh 

another thought as well,,, this ties with my dear friend's theory about fyo being able to jumpt to diff bsd timelines (stated in beast that only two people at any point given in all timelines can know about alt universes. other than fyo it would be beast zai which beast zai has confirmed.). my friend was saying how that everytime fyo died, he would jump/move his conscience into a diff timeline hence how he was able to live for such a long time... this kinda brought onto the thought that even current timeline dazai wouldnt be able to defeat fyo himself.. no longer human is zai's ability which allows zai to nullify other's abilities. but if fyo's ability is to transfer his conscience into others/alt timeline prior to being killed/dead.. that means even zai couldnt nullify it because, fyodor is fucking dead. which simply makes fyodor immortal/invincible.. which i dont really like the sound of cos that mid AF. like bro asagiri pull some better plot twist outta ur ass please  unless zai can nullify others abilities even dead. but like if ur dead then... how would u be able to use ur ability right ?? and if fyo does die (being impaled, stabbed whatever) theres a chance that his blood would come into contact with zai, which links back to the theory that fyo can transfer his conscience into other's prior being dead as long as his blood is in contact with them. (which obv kills the other person) which ngl .... thats pretty cool ngl... nother thought, i saw this tweet talking about the same fyoconscinece theory saying how being fyo killed/dying = crime and transferring his conscience to another replacing his own death with the other persons (the person who killed fyo dies instead of fyo) = punishmentthats a pretty neat thought yes yes.. .that would be cool...

some time long ago someone did also mention (again on twt) that crime and punishment were two different consciences living in one body... yeah idk where else to go with that...

also along with the fyoconscience theory.... kolya... my guy has literally bathed in fedya's blood, held his severed hand. bro's gonna be the next one to die... which makes me really sad because kolya's one of my favourite charas. he's so silly and goofy i love him sm.. he does not deserve to be manilupated by fedya. i will punch fedya if he does get manipulated....