Riku knew Sora well enough to know she'd attempt an attack eventually, and a combo didn't surprise him, though it was certainly harder to block. As such, he didn't push back like he did with the previous attacks, but focused instead on defense. The best offense is a good defense, after all...

As such he blocked one attack, using the length of his blade to place his arm pulled back. In a quick two flashes he's dismissed and resummoned his keyblade to wield it backwards, and swung his pulled-back arm forward in a slash.

A game of red-hands it was.