"Koikatsu Sunshine" revolves in the player (a male) going into vacation in a paradisiac southern Japanese island with his colleagues from an all-girl’s school with the objective to develop relationships with the girls.

The hero who lives alone near his aunt's house, away from his parents who have traveled abroad. He was moved to a female school with a male-female ratio of 1: many, where his aunt is the principal of the school. When such a throbbing school life has settled down to some extent, the hero is told a certain command by his aunt. It was a plan to use the summer training trip to get the beginner girls accustomed to romance.

The midsummer "Koikatsu" of the main character and the heroines will open!