Well if last week was patricide, today it's matricide, well since Natalia was a teacher and a mother figure to him.

But yeah, interesting episode overall as we get to see where Kiritsugu got his mage killing talents from and the things he learns from Natalia. In addition we see how he yearns to save as many as possible, haunted by the guilt and horrors of his childhood. He takes this principal to the extreme as you saw what happened, he doesn't love it one bit but he has to do it as he cannot risk the plane landing and spreading the infection further.

Natalia wants to live at whatever cost. Kiritsugu wants to remove the threat at whatever the cost. In the end Stinger wins.

Poor poor, bastard. Getting destroyed by his ideals bit by bit. His face at the end showed how bloody broken he was. I think I was kinda freaked out by the caster eyes.