Kinship fires on summon hit. On a piece that carries it it reads: Summon hits have a {chance}% chance to feed you {value}% of the bite as health.

Word for word it is Summon hits have a {chance}% chance to feed you {value}% of the bite as health, and the number in it grows with the gear: 25 to start, 1 more for every item level, at a 20% chance.

0 bases carry it.