Mc haves so many girls he can ask to do it with and even incest looks promising yet he’s too dense for any of that. Then when the mc is getting microscopically close to finding out, his sister comes in and be like “If I can’t have him, then no one can.” There’s always something stopping the mc of any series of any media (books novels, anime, manga, movies, tv shows, etc) from getting some pure romance. Like the ones where they go BEYOND holding hands.