I'm still not sold on FC, and I'm also kinda lazy so I'll mostly copy paste and old post of mine.

Assuming FC turnts out to be true and Asa is the war devil:
Stuff that I find contrived/contradictory in a strict sense.
>Why was Asa referred to as a human.
>Why did Asa recognize the faces of her class bullies, Yuko's, Denji's several times if horsemen are faceblind?
Stuff that I find contrived but could be explained by very convenient flashbacks.
>Why was Asa raised by a human mother that looked just like her?
>Devils grow up extremely quickly, why did Asa have a seemingly normal childhood attending school?
>Devils are naturally sadistic and violent, why Asa, the WAR devil never shown any violent/sadistic tendencies? even Nayuta had them, who raised Asa that managed to supress her nature?
>To add above, Asa would have slaughtered several people even as a child, if she did in an unseen flashback or something, why did she stop? why did she forget? and why isn't she deep in a PS vault because of that? can killing even be a deeply traumatizing experience for a devil?
Stuff that I find weird in a thematic sense.
>Asa being a devil goes against the coming of age elements of her character because a devil's nature is inherently different from a human, meaning that Asa's realistic teenage struggles are not real and she'll never live a normal life with Denji, they would never have children per example because devils can't reproduce.
>Denji ending up with the Horseman of War seems very random in contrast with him ending with a lonely human girl that mirrors him.
>If they're secretly the same, why do they occupy separate hemispheres of Asa's brain? and what's up with the imagery of Asa getting her skull split in half?
>Of all devils, why is Chainsaw Woman the War Devil?
That's all I can remember at least and it leaves aside all the stuff the story would be shooing away, such as the romantic triangle that Fujimoto set up (to my dismay).