My busty girlfriend was slept with by my father with a huge penis, and it wasn't a dream after all. (Nagi Sayuki, HBAD-592)

I started dating Yukino, who went to the same university as me. Yukino was cute, had a large bust, and was quite slutty. After dating for a year, I brought her home to meet my father. He looked at us tenderly, but I had no idea that he would actually make a move on my girlfriend...