He can't kill over things he doesn't know... Probably.

Nanako initially looks startled after the snow's impact, but after turning and seeing who was responsible she smiles brightly instead. "It's okay! I came out to play in the snow!" She brushes off her hair and shoulders to prove she's none the worse for wear.

"Are you playing, too?" She obviously doesn't consider it weird to find a teenager tossing snowballs at random people.