Chika enjoys her high school life by studying hard and swimming in her swimming club. Her two closest friends, Natsuki Komiya and Chizuru Aizawa, are her classmates and fellow swimming club members. One day, Natsuki and Chizuru discover a picture of Chika and Kaoru together, and they assume that he is her boyfriend. Finding out that Chika and Kaoru are living together at the Sakuraba Mansion, they demand to see Chika's boyfriend. And they come visit the Sakuraba Mansion on that Sunday.