Kimi no Kakera (Pieces of You) is by Takahashi Shin (of SaiKano fame). It follows two children as they search for the sun and themselves. Really good story, btw. We don't see storytelling of this caliber in shounen series very often.

This was a joint project with Mangascreener

October 31, 2007: Volume 3 has been completed, and MS has ended this joint project.