Tsukushite Agechau 5 ~Motomeru Otome-tachi~

Main character attends a boys school and worries about his lack of communication experience with girls. He looses a bet and infiltrates a girls school with a camera. He is chased and beaten by the guard, but is saved by girls in the dormitory. The four girls tend his bruises and are very kind to him. They kiss among themselves, but explain it as a greeting sign rather than expression of lesbian affection. Protagonist wants to be greeted in the same manner. He soon finds himself in love relations with all the four girls.

[From vndbreview]