Sei Yariman Gakuen Enkou Nikki

Based on the erotic game by Orcsoft Team Goblin.

Saiki Yasuo is a 45-year-old office worker. After 20 years of marriage, his wife asked for a divorce and left him. Now, depressed, he spends the nights drinking alone, until one night a girl from the St. Marian Academy approaches him looking for a client.

Note: A live-action AV adaptation (MIMK-014) was released on May 29th, 2013.