Haru Kaidou, the eldest son of his family, flies to Canada after hearing that his mother is close to death, only to find that she tricked him. Instead, she wants him to look after and "civilize" his adoptive brother Ren, a wild, antisocial boy who is more at ease with dogs than with people. Ren's distrust makes him hard to reach, and the two clash at first, but they grow closer as they come to understand each other. Haru promises that they will live together in Japan once he finishes high school. An accident then wipes out his memories of that summer, promise included. Five years later, Ren turns up in Tokyo expecting Haru to keep his word, but to Haru he is a stranger claiming to be his brother. The series mixes comedy, drama, romance and slice of life.