Moonlit Promises(2006)

Yakusoku no Tsuki

Roh is an outrageous orphan who has survived on the streets relying solely on his own strength. When he is taken in by a loving grandfather and grandson, Roh begins to believe that life may not be that bad. But when Seishin's grandfather dies unexpectedly, Roh finds himself responsible for more than just himself!

(Source: Juné Manga)