At first, Ace's explanation made Christian think that she was a little more insane than he'd already thought. But as he looked over what she handed him and really took in what she was saying, he found himself surprised. Not by her words as much as what they meant, underneath. That, and the fact that she had somehow always been this person and he'd never seen it before.
There was a thoughtfulness to her that he felt certain he must've noticed in passing or in the back of his mind, but he looked up -- really looked at her -- and understood that this was the sort of person that, evidently, would go to great lengths for people they cared about. Ace clearly loved Lily, whether that familiar love was registered or just an innate thing from undoubtedly spending time together growing up. He didn't know the details, of course, but he could see the outcome of whatever interactions made her care so much.
So he just nodded. "Okay. I'll read these over, then. I don't know how good I'll be at something like that, but, y'know, I'll do my best. We're not exactly close, but I do see her as a friend, so hopefully she thinks the same."