It procs off of Flurry (which can open a whole can of worms if it is considered a Melee attack)
Old (Concerning the implications of it being a Melee Attack):
Recently hit the ever loving shite outta a test dummy with only Rapid Strikes. Had skoria on (an 8% proc chance on DoT for comparison) and two axes (16% bleed chance). This is the results of 5 separate tests:
So it seems that the Twin Blade and Blunt Passive is still 'hand-crafted' code, and hasn't yet been updated. That or Rapid Strikes is bugged.
Edited by Avran_Sylt on August 8, 2017 5:53PM