The wealthy and esteemed Shiunji family consists of seven siblings: Banri, Seiha, Ouka, Arata, Shion, Minami, and Kotono. Arata, the family heir, is constantly teased by his sisters for his inability to find love. However, during Kotono's 15th birthday, the siblings learn a shocking, long-hidden secret—all of them are adopted!

The siblings all agree that their relationship will remain the same. But that promise does not last long, as each of the girls begins to approach Arata with intentions that go beyond sibling affection. Arata, who cherishes his family more than anything, must now find a way to protect their precious bonds and ensure that the Shiunji family never changes.

[Written by MAL Rewrite]