Cardcaptor Sakura, perhaps?
Also Harry Potter I feel crosses over pretty well if done properly. Like say having Wormtail turn up in gensokyo, given everyone except Sirius and Remus kinda forgot about 'him'.
Though there is the Weasleys, especially Fred/George.
I'd always liked the idea of Harry becoming a Youkai with subtle references to the main canon but few (not none) of the actual touhou characters appearing - exploring how the whole 'youkai' idea meshes with magic and people's beliefs about say Dragons in the wizarding community.
(Also seen a few where the Moriya Shrine turns up at Hogsmeade... potential for culture clash, etc... but unforunately none were good :V)
And in light of ULiL, potentially having wizards 'clean up' the aftermath (obliviation) of the danmaku fights in the streets of Tokyo and then begining their own investigations into the incident, and eventually, Gensokyo, doesn't sound like a bad idea either.