After spending most of his life residing in New York due to his parents' work, Yuito Kanzaki is moving back to Japan on his own. Unfortunately for Yuito, he has rather overbearing parents who also happen to be good friends with their boss. As a result, arrangements are put in place for him to move in with their boss' children.

The rather disorganized household that is to become Yuito’s new home consists of the four Ooji brothers—and is far from Yuito's ideal living situation. The eldest brother, Ousuke, is the natural sciences teacher at his new school and a dutiful elder sibling; following Ousuke is the frivolous Kaisei, a notorious playboy with a bad attitude; and the third son is the bright and friendly Hotaka who is always ready to lend a helping hand. These three young men, now with the aid of Yuito, all work hard to provide a good household for their adorable baby brother, Seishirou.

As Yuito begins to find his place as part of this odd little family, he quickly learns that things are far more complicated than they first seemed. Caught in a web of jealousy, passion, and sibling rivalry, Yuito is forced to make some difficult decisions—and hope he doesn’t tear the Ooji family apart in the process.