Tidus doesn't particular expect or think anything. Not even the small silence, he doesn't have time or - most of all - reason to think so. But if there wasn't anything he was expecting once Madoka does speak -

'Then--! I know I'm definitely not a baby-'

- nothing of what she actually says.

He's looking at her from the start, puzzled, and a puzzled state that doesn't leave him once she's done. The offer, and there's something so passionate or decided in it that...he doesn't get. Did he say something in particular? Is this some kind of cultural thing? Does she think he really wants to see a kid...??

"Wh, I... well, sure." But whatever the case, he's not going to not give her an answer, and that's a fairly...okay proposal he's fine with accepting. Brows still somewhat lifted, wondering. "So you mean- you want me to call you lil sis?"

Is this what this is a part of. Is he totally off the mark.