Why is this in the Most Unlikely Crossovers? The "Nyan Cat" song came from DaniwellP, a Vocaloid producer who made the song with Hatsune Miku (although there is a Utau Momone Momo cover which is heard plenty as well) as the voicebank.
Plasmapitch said: Actually, Nyan cat's song originated from a vocaloid so technically they're both japanese.
I think it goes like this: Vocaloid song is made (east)->Gets picked up by Americans, Nyancat.gif is made and set into this song (west)->Caffein makes this image (east again).