I think his lack of knowledge stems from his disinterest in the story. Some authors treat their stories like their babies but he said he never wanted to write this story and was glad to be done with it. When a story world become real a lot of details that didnt exist get filled in. Plot holes cannot happen in a real world so it will add things so that they make sense. For example an author can write X had a tragic childhood but not know why it was tragic.
I am curious as to what he mentioned were regrets regarding the story and if he can resolve them now. I also want to know more about the Villain's family but I don't think seeking them out before he has a certain amount of power is wise. A half demon from that family will be associated with his real family and he will basically be doxxing himself. His mixed family is currently on the kill list for both realm do he needs to hide his identity
Interesting read so far but I have one major gripe: MC is the author of the novel that he got isekai'd into, but, yet, he doesn't know anything about the demonic world he created or barely anything about his almost-ultimate villain?? Did he not flesh-out his villain or his motives?? Yeah, the author-MC, later clarifies he concentrated more on the heroes, but this is still your story and your villain is half-demon, so you don't know anything??
Now to the half-demon MC: I'm guessing he's between 16-18 years old. Grew up as a noble (??) in the human world judging from his home, so he didn't have any loyal servants to help him with his escape or to escape with him? Not one?? Did they all betray him?? Sad.
But now he's in the Demon Realm posing as a guard -- does he not have any demonic family? I know an ancestor of his committed treason and sided with the humans, but does that mean the whole family decided betrayal was the way to go?? I think it would be interesting to see if the MC had any demon family left and their reaction to seeing him.