"A special armor worn mostly by assassins. Its increased flexibility makes it easier for its wearer to strike vital points in their opponent's body."
Obtained From: The Keystone Monastery
Set Bonus: Increases Critical Hit Chance ? (Not Confirmed)
I've seen that my riposte (parry-counter) damage dropped from 322 to 215 when I broke up this set. That would imply a 50% bonus to critical hit damage.
Please test and edit if someone else can confirm this as well.