It's those words that make the smile slip for an instant. Not that he looks sad or anything though - no, if anything, Inigo mostly just looks surprised as he listens to Tidus. It's not like he thought Tidus was a bad guy and that's why his insistence comes as a surprise. No, it's just.. nice. 'I'm not letting you go out on your own.' That's exactly the kind of thing his friends would've told him back home.

Especially when it's followed up by that last part, turning it almost into a joke, a challenge.

"Am I really the one who has to be warned here? You just make sure you can keep up with me!" It's an obvious joke though. Inigo gets it. If he had fallen like that, he would've been more than just a little sore too. Hence why the jeer is followed up a smile with a softer edge to it. ".. Thanks for having my back though."