Also known as: 東方幼霊夢, 幼霊夢, YouReimu, 东方幼灵梦, 幼灵梦
A series of videos by Joyfull (Terrace) about a young Hakurei Reimu, her mother Sendai Hakurei No Miko, and Rumia from the past.
ReiReimu is its sequel series.
In fact, the proper name of Osana Reimu is YouReimu as the author said so.