Renai Kyoutei: Nukegake Nashi!

A childish student, Shirou carries a torch for his teacher, Oka. Masami, a good friend of Shirou's, who has cherished him like a brother, is confronted by Ryuuji, another friend of them, concerning his true feelings for Shirou. Ryuuji really loves Masami, but pretends to love Shirou, too, in order to attract the attention of the one he loves. Masami and Ryuuji conclude a gentlemen's agreement, in which either of them cannot hit on Shirou. Ryuuji orders Masami to substitute and take care of his sexual desire instead of Shirou. (Source: MU)