Cosmamania

Shuya Yamazaki is a high school student whose mother passed away when he was young. His father, a renowned archaeologist and adventurer, remarried the beautiful maid Midori. Shuya has a girlfriend named Wakaba, but they've never had sex. One day, he returns home to witness his father and stepmother in a compromising act, leaving him traumatized. The next day, on Wakaba's birthday, she wants to finally sleep with Shuya, but his shock prevents him from performing, angering her. Depressed and seeking advice from his father, who's away on an adventure, Shuya turns to Midori. She suggests he lacks confidence and experience, and decides to train her stepson in the art of pleasing a woman.