Why play a game if you're not going to, you know, PLAY IT? :/ And CRITICAL? What's even the point of playing that difficulty if you don't try and beat it yourself? Kinda defeating the purpose by having someone else beat certain parts for you. Just have your friend train up, like everyone else does.
I always train in Neverland before the Keyblade Graveyard, personally. The Unverse are strong there and give some nice experience, and you can do so at your own pace. I got from level 28 to level 40 within an hour on Aqua's story in Proud there.