Based on the adult manga by Shouno Kotarou.

My girlfriend is the daughter of an elite who goes to the Girl School. I met him in the Library. After getting to know him, we did a dating relationship. And I know all the secrets he used to do after school. At first I thought she was dying to pee, then I was surprised because she peed in the park. But, it turns out she was always doing masturbation in the park with porn magazines.

(Source: Nekopoi, translated)