[He waves one of his hands a little at the offer; he wasn't going to bring it up, but since she did...] It's okay, I already have a couple.

[As for why...well, he can't really blame her for being a little suspicious of a random stranger offering help, except he's just a very friendly stranger.]

Why...I guess because I think it's really nice that you're so determined to do something nice for your shinki. And because it's a game and you looked miserable, and you shouldn't be miserable playing a game.