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"...
Ever since then, his name 
and age are all he knows.
Er sagt, dass er nur seinen
Namen und sein Alter kennt.
Desde entonces, su nombre 
y edad es todo lo que sabe.
Desde entonces, su nombre 
y edad es todo lo que sabe.
À part son nom et son âge,
on ne sait rien de lui.
Da allora, le uniche cose che si ricorda
sono il suo nome e la sua età.
Depois disso, ele disse que não se lembra
de nada além do nome e da idade.