From Shoujo Manga Maniac:
On top of being a third-year middle-school student without a single relative, Riku Fukagawa has no memory of his life before he was ten years old. Memories of Family await him, even if they are not wanted, as a "phosphorus" identifies the cause of his peaceful life, and all on a certain day that two strange guys who call themselves brothers appear? But in Yamato, they manage the Jack-of-all-trades Hiyokoya, which is Riku's new part-time job...!?