Oh man, I'm pretty sure through Kikuo about 6/5 years ago! I've been listening to his stuff for a good while until I realized that he's not the only vocaloid creator and learned that Miku isn't the only vocaloid LOL, got back into vocaloid about a few months ago now _
My first encounter was waaay back in 2009. I think the first songs I listened to were Triple Baka and some others that have now been deleted from YouTube. Been listening mostly to vocaloid stuff ever since.
I believe I had been listening to some happy hardcore of some kind on YT (perhaps S3RL or Basshunter) and Masa Works Design's 'Fox Wedding' popped up in 'related to this video' section