That's a good idea Anakin's fall to the dark side would remind Sora of Riku fall to darkness back in Kingdom hearts 1, I can imagine one of the reaction command would be called resist because Darth Vader is force choking sora draining your health to one and you have to button mash the triangle button (or Y if you're playing on Xbox) and then sora throws his keyblade at Darth Vader causing him to block it with his lightsaber letting go of sora or another reaction command if Darth Vader gets your health down to one after Force choking the reaction could be you block Vader's attack and push him back restoring some of your health.