[He doesn't get what she's trying to say at first, but the bright-eyed expression says everything that needs to be said.]

...I don't know. I don't know if it's possible to go further back in time. It... might be, but I won't know for certain until we can rebuild the machine that brought me here.

[Bringing Kamina back would be incredible; they certainly could have used his help, but he doesn't want to promise anything when he has no idea if it's even possible.]