Finally decided to fight the strongest boss in makai kingdom today, ended up beating him in two turns with some combo boosting and attack buffing.
Needless to say, some characters died in between turn 1 and turn 2 since post game bosses in NIS games are very nasty and require lots of leveling and taking advantage of the game's mechanics to stand much of a chance.
The best vehicle in the game, Yoshitsuna is the reward beating the fight. It's basically a battleship with lots of item capacity, jacked up stats, nukes, and a giant, pinkish purple planet destroying death laser of doom.
Unfortunately, main post game content I have left involves random dungeons which restrict vehicle access, so although I can try gearing it up with the best items, I won't be able to abuse it as much as I'd like. Still very fun to mess with though. XD