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"...
There are still lots of things 
I need to do with you.
Wir haben immer noch einiges
zusammen zu erledigen.
Aún hay muchas cosas 
que tengo que hacer contigo.
Aún hay muchas cosas 
que tengo que hacer contigo.
Il reste encore plein de choses
à faire ensemble.
Ci sono ancora un sacco
di cose che voglio fare con te.
Ainda tem muitas coisas que
não fizemos juntos, não é mesmo?