TIME STRIPPER MAKO! How could I forget that one! It was my second hentai game ever (Pia Carrot doesn't count since it was in japanese).
Girl goes back in time to prevent another girl from stopping the Hentai Guy from getting together with his girlfriend, since he's her ancester.
This game is WACKY. The villain girl, Non/Noin has an atomic hammer.
Also, first instance of girl with a dick that I remember.