i think this was on hentai from hell entitled "his first time was with his friend's mom", i think it was a rewrite cuz here he says aunt

No, it's a misnomer. Technically "obasan" does mean "aunt", but it can be used for any woman in/past her mid-20s by someone younger.

You'll find the same thing with words like "oniisan" and "oneesan" ("older brother" and "older sister", respectively, but usable for a young adult by a younger person).

This isn't a rewrite, nor is it incest.

wow awsome *w*