Having come to Canada upon hearing the fake news that his biological mother Haruko is in critical condition, high school student Kaidou Haru meets a young boy named Ren. "You have a new brother. Take care of him." So instructed by his mother, Haru is forced to spend the summer with Ren. 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"...
Oh, it's just that these two are special.
Ach, es ist so … Die sind
für mich etwas Besonderes.
Eh, es que estos dos son especiales.
Eh, es que estos dos son especiales.
Oui, ces deux-là sont différents.
Oh, è solo che questi due sono speciali.
Oh, me desculpe. 
 Esses dois são especiais.