Nocturne's done.
The big man went down easily enough, but I had to fuse up one hell of an A-Team to do so. Outfitted my main character with Freikugel (insane skill; so much better than Spiral Viper as far as single target damage goes. Plus the animation is way cooler too.), Tarukaja, Rakukaja, Repel Ice, Repel Fire, and Endure for the last fight, and it worked pretty well. Dante, Lilith, and Micheal just wouldn't cut it as allies, so I had to upgrade. A souped up Daisoujou replaced Lilith as the group healer, made HAWKESOME by the sacrifice of the Pixie you get in the Labyrinth. Metatron became the new buff/debuff demon, having Debilitate, Tarukaja, Makakaja, and Rakukaja. And Dante was replaced by a nifty Beelzebub I fused up, which had Pierce and Focus, allowing him to dish out insane amounts of damage.
Endure on both the main character and Daisoujou was pretty clutch. Would've lost the fight in two instances were it not for that skill saving either the healer or the main character. Also helped that every demon had Debilitate, and everyone, save Daisoujou, (main character included) had Tarukaja/Rakukaja, so that if the big man used some sort of dispel skill, the buffs/debuffs could easily be put back up in short order.
Excellent game, mostly owing to the superb way in which you can develop your party, the fun dungeon crawling with random encounters that actually pose a serious threat, and the cool boss fights. Great fun except for the slightly annoying task of trying to make sure certain skills weren't inherited (no, I don't want my new superbeast to have a move as bad as Bufu) and that goddamn Preta. Fuck that guy, he killed me more than any boss.