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"...
I'm so sorry, Ren.
Tut mir wirklich leid, Ren.
Lo siento, Ren.
Lo siento, Ren.
Je suis désolé, Ren.
Scusami, Ren.
Me desculpa mesmo, Ren.