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"...
Don't you have plans with your friends?
Aber du hast doch mit deinen
Freunden was vor, oder?
¿No tienes planes con tus amigos?
¿No tienes planes con tus amigos?
T’as prévu des trucs
avec tes potes, non ?
Non hai organizzato niente
coi tuoi amici?
Mas você tinha um compromisso 
 com seus amigos, não tinha?