Well I always knew it but my sister was way way ahead of her time. I suspect that nobody in the rave world knows what poiballs are but it’s a new thing in rave dancing. Swinging balls around on strings. Click for video in Harajuku.
What they probably don’t know is that this is an ancient Polynesian thing. My sister used to learn this at Hula class. She could kick this guys ass. She would usually do 4 balls, 2 in each hand going opposite directions.
Originally they had rocks on the ends and were used for war and hunting. Ouch! They hurt even with just cloth on the ends. The streamers are a cool edition though. 
Update: Tami sez (5 balls, one on her right foot held by her toes!)
The guy in the video probably a beginner based on some of the people I’ve seen.
This is now done with all kinds of glow toys and called “Glow Poi” or with special Kevlar wrapped wicks and called “Fire Poi”. If you are seriously into learning more about the moves you should check out Sperculism’s Online Community and if you’re more interested in fire poi specifically you should check out Luxotica Fire Toys.
Cheers,
Fireguy