During his father's funeral, Shogo is startled by a voice outside his window that claims to be that of his little sister. However, before he can learn who it is, he finds out the conditions of his inheritance.

Shogo receives a mysterious call from a person who claims to be his sister. Meanwhile, his school life gets a jolt with the arrival of a new student to his class.

Shogo's sexual preferences come into question, causing Miyabi and Rinka to overextend in their efforts to show him the appeal of a woman. The next day at school, he tries to avoid them and hides in the student council office.

Shogo tells Konoe that Miyabi may be his little sister. Ikusu later contacts Shogo to inform him of a phone with voice-changing capabilities which may be connected to the calls he receives from the mysterious girl claiming to be his sister.

Shogo is constantly being awoken by his supposed little sister early every morning, much to his annoyance. Sleep deprived, Shogo is unwittingly invited by Mei to sleep with her in her secret room at school, much to his uneasiness.

After Mei is told by her adoptive father to come back to Massachusetts due to her shop failing, Shogo concocts an advertisement plan to prevent the Lyrical Sisters from shutting down.