Kingdom Hearts II What part in KH2 did you NOT undertsand?

Something about the energy from the machine purified the darkness in Riku's heart, eliminating all but the most basic of his darkness abilities, Dark Aura and Dark Shield. He essentially lost Xehanort's powers and could no longer call on them.

I think, anyway.

 

I'm not confused about it any more, but I wondered for wuite a long time why Roxas asked Sora "why he picked you" when they fought eachother... It ws kind of... unexplained :P
But now I get it.