Kindling Eye fires every so many crits. On Cinder Charm it reads: Every 5th critical strike ignites the target for 50% of the hit.

Word for word it is Every {count}th critical strike ignites the target for {value}% of the hit, and the number in it grows with the gear: 60 to start, 4 more for every item level, and it only goes off every 5 times you set it up.

It leaves Burn behind, which makes it Fire build material.

7 bases carry it, and 2 Uniques are built on those: Summer's Last Ember and Heart of the Furnace.

Awakening can reach it too — 11 spirit paths pick it up at Spirit Level 3: Emberflow, Blightweft, Ashcall, Scorchedge, Flaretyrant and Emberfang and 5 more.