Ore no Kouhai no Futokoro ga Fukasugite Kowai.

Kazuma's just your regular office worker… Except for the fact that he likes playing with his ass so much, he's been holding off on masturbating for two weeks. One weekend, on the way home from one of his usual self-loving sessions in a soundproofed, easily-cleaned hotel room… he happens upon his junior colleague Maruyama and gets roped into drinking with him! Later, when carrying a passed-out drunk Maruyama to bed, Kazuma catches sight of Maruyama's raging boner!