Some people have the idea of Felix being all shy, weak or just being like a puritan virgin girl, but I beg to differ.

Facing this hardcore woman and convincing her to take him with her.

I don’t think you need an explanation for this. First she keeps punching him in the face, him recieving them with a smile. Then he pulls them BOTH out of there. He barely reaches her hips and could hold her, armor and all like it was nothing.

Look at this. At first of course he’s nervous but that’s because he just kissed Calhoun on the cheek without permission or warning, and if she went bonkers when he tried to flatter her calling her a “dynamite gal”, just imagine what kissing her would do. She’s going to kick his butt, and he already saw her punching Ralph in the face when mad; she sent him to the floor.
After she kisses him, he’s surprised. I would be surprised too, honestly. (Weren’t you going to punch me, ma’am?) But do you see any kind of doubt or fear after that? “OMG what’s this? what’s happening? what’s kissing? are this lips” HELL NO, he smiles, cups her cheek, tilts his head for better access and responds to her kiss like a boss. He knows the drill.

Now here you might say “But they didn’t just marry after the events of the movie, it probably had passed like months or whatevs” but still, this is something that just confirms the behavior of the other kiss.
HE TILTS HER. Do you know how hard is that? And the perfect coordination of his hands so he can catch her gently as she falls. He pulls one of her arms and with that hand he holds her head while the other holds her back. And then, the sweet confident kiss. Perfect.
As for the rest of the move, he’s being a gentleman and most of the time has no idea what’s going on so of course he’ll look confused. And he’s just so nice with everybody, that doesn’t mean he’s weak or that he won’t defend himself in case of needing to.
“Felix doesn’t know how to shoot a gun.”

I rest my case.