Responses
I keep wondering why this is R-rated on the official site, it doesn't have many bloody scenes, even Chasing Tails was more violent and it didn't need age verification. So maybe it's because like you mentioned they will have a physical relationship? What we have seen so far in the story doesn't make it R-rated.

Don't tell me he will start having physical relationship with her and later she end up having a child with him and now she have to protect that child from him or something. Like time skip to some years later and her brother will come out of the jail and everyone she knew gets a different life. Who knows. I know this won't happen but the only thing someone knows is the author and god