They're origami people (in an abstract style... not quite as abstract as the brilliant one fold stegosaurus). Here they're being used for nagashi-bina... dolls you put your curse into to float it away down the river. In Gensokyo, those naturally end up with Hina, because that's her job. IIRC, in one of the books Hina requested that people don't bother with the fancy dolls because paper ones will do.
