Fury fires on melee hit. On a piece that carries it it reads: Melee hits build Fury: +{value}% Melee Damage per stack up to {count}, fading 4.5 s after your last hit.

Word for word it is Melee hits build Fury: +{value}% Melee Damage per stack up to {count}, fading 4.5 s after your last hit, and the number in it grows with the gear: 1 to start, 0.02 more for every item level, and it only goes off every 20 times you set it up.

0 bases carry it.

Awakening can reach it too — 6 spirit paths pick it up at Spirit Level 3: Shiveredge, Miasmaedge, Cindershade, Rimefang, Voltshade and Venomfang.