The hope is fulfilled: with no defence and the block stunning him (or more his ill-preparation on what to do next), the jab throws Tidus off-balance from the top, his weight below unable to catch him, and so he promptly topples.

Unsurprisingly, Tidus sits dumbfounded, the sting from his landing shooting him awake. He throws a stunned look at Tifa, but promptly understands what’s occurred and why. So he picks himself up from the floor, shaking out his arms and, this time, he bounces on his step, a brief thing before he comes in this time with a quicker fist.

There’s inexperience to his moves, knowing where to aim; he doesn’t know how to read a hand-to-hand fighter, but he does have nimble reflexes, knows to use his secondary arm to defend (but probably not from throws) and has speed when he’s actually trying.

But he’s still hurt, his mind not in the right headspace, and so the frustration quickly builds into a voice at the back of his throat, thrown out first before a punch:

“I couldn’t have saved her, could I? After everything--”

And when he does throw it, it's with sharp yell, angry and hurt, as if wanting to punch that belief.