In 1993, the NHK (one of Japan's major broadcasters) broadcast, unscheduled, a short (probably around seven minute long) animated clip on their BS-3 satellite system.  It's generally agreed to have depicted some sort of comedy about young female mages attacking each other with magic over trivial slights and misunderstandings, in a mythical isolated part of Japan called the Illusion Village.  Why this happened is unknown.  The NHK has not responded to any questions about it - more likely than not they just don't care - and the exact contents of the clip have not apparently been recorded, as is the case with many such old (pre-widespread internet use, at least) animated shorts.  Nonetheless, this was apparently the beginning of the "Touhou" phenomenon.

Something about the clip seemed to captivate many of the viewers who happened to see it.  Previously upstanding young students and workers abandoned their duties and hopes in favor of investigating the popular cartoon and comic media worlds of Japan.  In a short time, many of these, somehow convinced that they could draw, began to produce fanart of the clip.  Many didn't remember the source, having been too young at the time, assuming that they had come up with original ideas, or, as time went on, that they had somehow noticed one of the other fan artworks that already existed.  As this was happening as the internet came more into the public mind, they soon congregated their in cyberspace - hundreds of individual communities, small and large, often unaware of the full extent of the others.  And always producing more and more pictures.  Images of all sorts, costumes, musical 'remixes'.

In much the same way this has continued to the present time.  Actual stories to go along with the half-remembered characters, ill-defined in appearance and self, have appeared.  Successful series of fighting as well as puzzle and "shoot 'em up" games have appeared, along with legions of fan comics ("dōjinshi"), written fiction.  Rumors of an opera in the works are unsubstantiated, but there's not much reason to doubt any more.

Images with the "touhou" tag are part of this unknown instrument.  Please remember to maintain artist metainfo and other proper attribution mechanisms.