Quote Originally Posted by SeeDRankLou
Fight Xemnas for the first time, not including Kingdom Hearts I, but rather, in the WtNW's duel in the Darkness, after the other OXIII are dead.

This is TECHNICALLY the pre-requisite for the Cup, just to give a more accurate impression of how far or close you are to the actual unlocking the Cup, but SRL is still, in essence, 119% correct. He's not 120% because there is a 0% room for a margin of error, which is also dictated by a 2% margin of error.