I'm reet cheesed off with dying last night and I've sucked up all my resources - mainly the magic potions so I'm running out of options for spamming the big magic spells. I think I'm stuck in the final castle too so I can't get the hell out of there and go buy some sheeeeet. OR CAN I? I've no idea. You know how hard it is to fight your way from one checkpoint to the next? Lots. Lots hard.
Yes, and I'm ashamed to say that I had a peak at a walkthrough last night. Well I'm on the last boss for christ's sake, I can treat myself can't I? But it really doesn't mention whether you can get out of there and, hell, it was as long as any book so that doesn't bloody help. Plus it gave the distinct impression that the last boss is a piece of piss which is patently untrue so, y'know, fack you people who write walkthroughs. We can't all be awesome at RPG's so stop pretending like I know how to juggle stats and shit. Y'know what I actually do - tool everyone up with the biggest getup they can wear and sell off the tat for potions. WELL IT SEEMED SENSIBLE TO ME. Anyhoo, I got this far so I must be doing something right. But anyway, that Ni No Kuni... it's pretty compulsive stuff.
They do generally expect you to have followed the walkthrough and so be in the same position, which may make the last fight easier than you're finding it.
Not having played this, I can't offer specific advice, but I'd be surprosed if you can't extract yourself from the current situation.