Shinjuu Suru made, Mattete ne.

When he was a child Fukuta had his much loved Aoi-niichan, but for some reason he forgot all these years. He woke up from his dreams about the past crying without understanding or remembering why. Until one day Aoi appears in front of his door bringing with him a huge mystery.
Note: Volume 1 contains a side story and a prologue chapter.