After the death of their parents, Akito Himenokouji and his younger twin sister Akiko were adopted by separate families. Six years later, they now live on their own, under the same roof.

Akiko makes no effort to hide her brother complex. She even goes as far as trying to convince her brother to make their first night together a memorable one, to no avail. Akito calmly rejects his sister's many advances and deems loving his blood-related sister impossible. However, Akiko is determined to prove that love can overcome any obstacle.