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 no secrets between 
Haruko-chan and me!
Zwischen mir und Haruko
gibt es keine Geheimnisse!
¡Haruko-chan y yo no tenemos secretos!
¡Haruko-chan y yo no tenemos secretos!
Il n’y a aucun secret
entre Haruko et moi.
Tra Haruko e me non ci sono segreti!
Não existem segredos entre mim e a Haruko!