Last boss / fiend killed - Seraphs trio / Trumpeter so it's time to finish the Kalpas 3rd, 4th, 5th. I hope 60+ lvl team will be able to take out Beelzebub.
You haven't done the 3rd Kalpa yet? I always did Labyrinth levels (and Fiends) as soon as they were available; the "extra" content is generally much more interesting and I wanted to experience with as little level advantage as possible.
You'll probably stomp through the Third Kalpa, though I'm certain one sequence will give you some fits. The 4th Kalpa is probably the best dungeon area in the game. Going into that one blind was a bit of a shocker; I had to bust out the grid-paper in a few instances. Good times. Very good times. The boss of the fourth is pretty excellent as well. He killed me twice, once with his signature attack and once with his propensity for Focused Criticals aimed at the main character. And when I did beat him, it was by the skin of my teeth. Given that you know who he is, he probably loses a lot of his edge, especially if you spoiled yourself on his abilities.
The Fifth Kalpa is kind of a letdown. The dungeon design is much less interesting than the Fourth and the boss in there isn't too difficult either...well, the guy you can pick up in the Fifth Kalpa sure makes quick work out of that floor's boss (he joined easily for me; I guess that's one of the good things that can be taken away from having played DMC2).
Nocturne's difficulty is really overrated by a lot of people. It's mostly because most JRPG players abilities has been completely hindered by the dead easy difficulty of Final Fantasy that Nocturne seems super tough, when in reality battle strategy is only slightly harder than FF (except for gimmick bosses)
Like Dark Souls, the difficulty of Nocturne is greatly overrated by casuals but also underrated by the hardcore crowd. If you go through Nocturne with minimal spoilers* and grinding it will present a good deal of difficulty on Hard mode. You'll be punished for mistakes and improper preparation, but most fights have at least a couple of "solutions", so it isn't merely trial & error. Dungeons, and the numerous encounters therein, will tax your resources and provide a challenge...unless you get cheeky and slap Mana Refill on a Mitama around level 40ish
. But even that isn't all that broken in terms of obviating resource mechanics in blobbers given the high random encounter rate in dungeons (even with Repel constantly active).
I can't think of many RPGs more difficult that don't rely on randomization, reflexes, or extremely cheap/linear gating encounters that are harder. Certainly Nocturne isn't the hardest game, but it's definitely on the right tail of the RPG Difficulty bell curve.
*The only real spoilers I had were some vague hints:
-"Keep the Pixie"
-"Do extra content as soon as possible"
-"Get all the Magatama"
and a fusion chart.