Aniki to ore 2: Moeru kikumon (2004)

The second in the gay movie "My Brother and I" series. Kotaro, a high school student, has a stepbrother after his sister gets married. However, he turns out to be Ryoichi, his homeroom physical education teacher, whom Kotaro has a crush on. Kotaro learns from Ryoichi's friend Kasama that the two were sex friends in college.