During his father's funeral, Shogo is startled by a voice outside his window. The voice claims to that she is his little sister, but 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.
Kunitachi might be the Shogo's sister but he can't get close to her. Ikusu suggests that Shogo and Kunitachi spend time outside the school to have her drop her guard.
Things get messy when all of Shogo's potential wives are invited to the same party. Just when he thinks things can't get any worse, he learns that a trusted family member is plotting to overthrow his inheritance.
In the aftermath of the turmoil about who was Shogo's true sister, Miyabi sets up a dating contest for the rest of the girls to see who would be worthy of dating Shogo. She constantly interrupts the dates due to jealousy until Konoe brings the three of them to an amusement park.