Fate/Zero (2011)

S2E6 Where Justice Dwells

Natalia has been Kiritsugu's guardian ever since she pulled him from the island's wreckage, shaping him into a ruthless killer with every lesson she taught. What began as a mentor's duty slowly blossomed into the fierce, unbreakable bond of a mother and her son. But now, Kiritsugu must make a choice that will sever that bond forever...