Why Is a Pikachu Army Forming in this Video?!

I honestly don't know what to say about this, this is like a nightmare of some sorts. This is video footage of a Pikachu army gathering together in in Akarenga Park, Yokohama. But for what?! Are they preparing for a Pokemon battle, or to take over the world? Why is this happening?! I'm a little scared. 

Via: Geekologie