bandoned by his father as a boy, Yuta grows up as the foster son of a restaurant owner and takes over the restaurant at the owner's death. Cheery, always smiling, always helpful, Yuta is known as Yama-chan, the friend everyone turns to. When Yuta discovers he had a hitherto unknown baby brother, he sets out to track him down. But the baby brother, Yusuke, has grown up to be half of a successful comedy team, the Kinjo Brothers, and Yusuke's professional "brother" has just written a best-selling book about their adventures growing up together. Yuta's appearance on the scene threatens to reveal that the book is a complete fiction and to set all three "brothers" into conflict with each other.

Overview from themoviedb.org