TSA writes: “While the Captain Americas and Marios of the entertainment world are guarded by strict copyright laws and armies of lawyers, one of the best known and iconic video game series in Japan does not play by those rules at all. Touhou started out as a humble series of flashy indie bullet hell games, coming from the imaginative mind of ZUN, but its blossomed into a multimedia phenomenon thanks to ZUN allowing his world and characters to be used freely by any and all creatives, so long as hes simply given an acknowledgment credit.”
Source: N4G PC Touhou Mechanical Scrollery Review (TheSixthAxis)