Shimajiro, who helped an injured baby whale Kuu-chan, takes care of Kuu-chan who wants to return to her mother and keeps her in touch. In order to return Ku-chan, who was about to be sent to the aquarium, to her mother, Shimajiro rides on her back and sets out on a journey toward the southern sea.

Due to an error the male student Kagami Yuuki is registered for a room in the girls dormitory of his new co-ed high school. Since no male rooms are available he is left with no other option than to sleep in the girls dormitory in the same room as the teacher that made the mistak in the first place, Ayane-sensei. To avoid getting kicked out of the school for being a boy in a girls dormitory he has to cross-dress whenever he is leaving his room. Needless to say that this brings him a lot of trouble.

Shimajiro, who helped an injured baby whale Kuu-chan, takes care of Kuu-chan who wants to return to her mother and keeps her in touch. In order to return Ku-chan, who was about to be sent to the aquarium, to her mother, Shimajiro rides on her back and sets out on a journey toward the southern sea.