"Hey, my name is Xemnas, nice to be creating you today. You are going to live here with all these rest of us black-coated people. Yes, this is Nowhere. Literally. Where are we? I don't $%&$#* know. Anyway, this is Roxas, and he's going to be helping you do your job. Oh yeah. You need to gather hearts for us while we sit around here and sing songs, sulk, think, and just generally do nothing. Hm? Oh, sure you can leave. Did I mention we are in the middle of nowhere? Just making sure. By the way, not going to tell you what you are. But I know. And he does. Him too. So, enjoy yourself."
PS. I'm pretty sure he ordered Axel to do the dirty business in Castle Oblivion. If not, he ordered Saix to order Axel.