Imagine. ventus and aqua battle terranort. defeat him. forcing xehanort out of terra's body. now terra can become a guardian of light. xehanort is now 1 darkness short of 13. who does he choose to replace terra? ROXAS. imagine, if roxas was a darkness it would surely affect both sora and ventus making them at the very least uneasy and putting there heads out of the game. it would be an incredibly good plot point.