How comes, that I have it on easy? I don't know, how I got it, but I have it, and definitively not playing on hard. EDIT: I'm not even sure about the price, don't recall to buy something for 100.000 gil Maybe it was a bug or something, but I really have this garb and even cared it into NG+ (and on easy again, I'm not brave enough for hard mode, even not for normal).
There was an Outerworld Challenge that unlocked it for everybody.
Oh, right, I did a little searching about it, there was a NPC - a dog with a name LRFFXIII, with a blue orb before his name, which I believe I've spoken with and the garb unlocked in the reward menu. Wouldn't be a bad idea to include this way of unlocking, as people could be confused (like myself).
I'm not allowed to talk to ya, all i can say, that I'm not allowed to talk to ya.