Riku is only playable towards the end of Kingdom Hearts II, for a short period of time. During the final boss battle against Xemnas, Sora is captured and Riku must stop Xemnas from destroying him....
You can only play him once, and that's when you and Riku are fighting Xemnas for the last time. Sora get's captured by Xemnas and you have to use Riku to save him
when sora gets trapped by final xemnas you have to use riku to free him, that copy that xemnas does is quite frustrating you need to attack him or he will push you back to the start and you will not...