Chichi wa Shiranai, Boku to Haha no Futei na Kankei The Motion Anime

The heroine's half-son is already at the age when the opposite sex occupies all his thoughts.

He began to experience unfamiliar feelings after seeing the gorgeous body of a beautiful woman brought by his remarried father.

One night, unable to control his urges, he decides to have a little peek at his stepmother while she takes a bath.

He feels guilty, but masturbates furiously.

However, an unexpected call on his phone reveals him.