As a high school teacher, Chris Watanabe unexpectedly gains an English step-brother named Wataru when his father ties the knot again. However, tragedy strikes when their parents pass away in a plane crash soon after Wataru transfers to Chris' school, leaving the two step-brothers to live alone together. With a striking contrast in personalities - Chris as the cute elder and Wataru as the cool younger - the duo embark on a new chapter in their lives. What adventures lie ahead for them?