ironically, i'd seen few people in DL fandom especially on tumblr, ship cordelia and ayato, which on my opinion disturbing.
mother son relationship is one thing, but most eroge use siblings relationship. which is disturbing too.
it is hard to find overpower main character since some mangaka try to give them as much flaw as they could.
but on top of my head is Fushigi yuugi.
i think tamahome is fairly overpowered, and their main antagonist is one of the most overpowered character i ever known
i've seen some otome games that brings out this issue.
so the question here, is it a big NO-NO
it is just game, so chill.
example: sakamaki laito with her mother cordelia.
i'll be happy if you include other example