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"...
When I lost the whole foundation 
of my happiness in one instant,
cuando perdí los cimientos de 
mi felicidad en un instante,
cuando perdí los cimientos de 
mi felicidad en un instante,
C’est quand les fondations du bonheur
ont entièrement disparu
Quando in un attimo le fondamenta
della mia felicità crollarono,
Quando, em apenas um instante, perdi o alicerce...
Que sustentava toda a minha felicidade....