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"...
B-But forget that! It's Ren!
A-Aber es geht um Ren!
¡Pero olvida eso! ¡Ren!
¡Pero olvida eso! ¡Ren!
Mais Ren a disparu !
M-Ma c'è un problema con Ren!
E-esqueça isso, é sobre o Ren!