So, Star Ocean 2 has a pretty famous trick where you can get something called a Counterfeit Medal, which you can use to set the experience a character needs to level up to 1, with the effect working until you hit level 100. You can then use the Replication skill to duplicate this medal, letting you reach level 100 off literally any enemy type you want.
Later on you can get an accessory that gives you 1 experience per step taken on the map.
I think you can guess how my endgame grind went based on the combination of these two things