very well-written with a plausible theory, i agree with you
about that grown eve thing, i couldnt help but notice that he had gozu's face. it makes me wonder if maybe they will somehow fuse together, or have a son. if i recall correctly, gozu was at risk of getting mpreg while doing it in a magic costume. that would be really bad tho, since gozu said that the moms of eve's children explode :S
I totally forgot about that, but something tells me they might go ahead and get him pregnant. If it’s not in the main story, then I’m a side story.
╮(￣▽￣)╭
What if Eve is becoming the Saintess, like Gozu mentions? All of the conflicts that were supposed to happen after he turns into the demon king are being conflicted by him before he turns into the demon. He's still meeting the people, but instead of something tragic happening bc of him, positive things are happening. So instead of doing "Demon King Things", he's doing "Saintess Things" and that is starting to show in the environment.
Now onto the stretch of my theory. What if the "Good Guy" kidnaps Gozu or something happens to Gozu? Eve would spazz the fuck out.. The author already showed use what Eve's 'grown' or Demon King self looks like. We can also see that he can barely stand people being too kind to Gozu, and it seems like his possessiveness is just growing by the day. Now whether Gozu leaves willingly or unwillingly or he just simply gets hurt, that would be more than enough provoke Eve to act more evil, more Demon King like.
Now to stretch even more.. if Eve is really becoming the Saintess, then there wouldn't be anyone to stop him if he was to become the Demon King. The Hero can't stop him because he no longer has the blessing of the Saintess, her health capabilities, or the power of friendship. If no one is able to stop Eve if he goes batshit crazy, not even that one magician, then the story is gonna go boring. I think Eve will have both titles and all the abilities from both titles. I also think the author will either pull a "Magic of Friendship Will Fix All" cliche ending or give Gozu the power to help Eve come back to his senses, since it seems like when he (Eve) is in heavy thought Gozu is the only one to really bring him back.