Having arrived in Canada during summer break upon hearing the fake news that his biological mother Haruko is in critical condition, high school student Haru Kaido meets a young boy named Ren; his new adopted brother, and is forced to spend the summer teaching him how to act and behave so he can fit into societal standards. Every day is a battle with Ren, who refuses to listen to anybody. However, as Ren grows to like Haru little by little and Haru comes to adore Ren as well, they make a certain "promise" to each other...