Yuuji Nakagawara works as a history teacher at an all-girl school. There, he meets the director's daughter Satsuki Sakuragaoka. They soon become friends and get married.

After that, Yuuji decides to live with his wife's parents. Satsuki is the second daughter of the three sisters, and her eldest and youngest sister, Yayoi and Hazuki, also live there.

They began living together under the same roof. As his wife's sisters start acting weird towrds Yuuji, he ends up deepening his relationship with them.