You mean you've prepared yourself for killing a bunch of people who don't know how to fight a Servant. [ She says it boldly to reaffirm that in his mind.

The loss of that smile of his only encourages her to try to sway him into not fighting. As futile as the gesture may be, it's all she has for now. ]

I've studied wars and battles all my life. I might not have experienced much of them and it'd be childish to say the war I was in was worse than yours, but to disregard my experiences just because I'm a child who has lived in a cushioned time is a grave mistake, Lancer.