The Ultimate Masturbation

アルティメットマスターベーション しごきの山

Also known as Ultimate masturbation: Shigoki no yama

A straight graduate student goes to the masturbation camp in the mountains held by the "gay masturbation charisma", where all sorts of masturbation techniques are tried out by participants. One day, the student is raped by a gay guy at the camp, and he starts to question his belief in masturbation.