The manga was about a young girl (like maybe 10 or so?) who has the memories of a girl that died while saving her mom who was pregnant with the young girl. She winds living next door or near the dead girls boyfriend who is in his mid 20's. She actually falls in love with him and tells him when she is still young, he rejects and life moves on a little till she is now a teen-ager. Something happens and she confesses again, and he accepts her feelings (it seems he does at least) than she moves away and her new high school teacher is the dead girls younger brother...phew.
Sorry it seems very confusing, but I must find it! Please help!!!