I discovered Nightcore in the deeper ends of Youtube the other day, a fascinating sub-genre of trance that seems to be mostly based on and around Youtube, and where the defining quality of the genre seems to be remixes of popular songs with an increased pitch and tempo.
While every Nightcore song seem to contain stills of Japanese anime, Vocaloids or similar, almost all songs are western, and it being based on Youtube also implies that it is a phenomenon mainly based in the US or Europe. If I had to make a more precise guess, I would guess that the epicenter of the phenomenon is in the US, mostly since I find relatively few remixes of very European music, and with the obvious exceptions, relatively few Nightcore remixes in languages other than English.