One day, as the boys Aoi and Hajime are returning home from a school picnic, they find an abandoned little boy in the park with the note "please adopt me" pinned to him. His only possession is a small backpack with a change of clothes, and the nametags on his little boots read "Gaku". Both Aoi and Hajime want to adopt this "little brother", but Aoi wins when Gaku chooses him over Hajime.

Ten years late, Gaku has grown into a handsome boy with no memory of his adoption. Gaku and Aoi are close as siblings, but Aoi finds himself feeling more than that for Gaku. Hajime has always been in love with Aoi, but sees that Aoi has eyes for Gaku, and vice-versa. Gaku and Aoi are hesitant to express their feelings, each fearing that the other holds only a brotherly affection. They one day, Gaku finds out about his adoption, and that he and Aoi are not related by blood...