The level 99 trick involves dying after this level increase, and then repeating the process over and over until you get to level 99.
This is rather tedious, but there are methods to make sure things go smoothly. Blue Moon has created a step-by-step process for this levelling trick.
Once you are in chapter 4, visit the armory (This doesn't work in previous chapters). There, speak to Dominick and try to buy some armor. Once you are at the menu, press the triangle button, This allows you to buy armor for someone who is not in your party.
Keep buying, even if you are about to run out of money. Keep buying even when you do run out of money, because apparently Dominique doesn't mind. Keep buying the most expensive stuff. After that, sell sll of the expensive stuff... Then spend it all on other expensive stuff, like honing your weapons. Then repeat the process.
Hopefully they won't fix this in the US version.
Some spells to try this on are Eternal Wind, Hellfire and Final Flame.
Hex S + Hex x 4 = Blue glow in room, Hex Dolls' eyes open and glow yellow
Knight S + Knight x 4 = Green glow and all knights have sword raised instead of down
Goddess S + Goddess x 4 = Blue glow, Goddess statues turn their urns upside down (like pouring)
Goddess S + Knight x 4 = Red glow and all knights face the goddess
Goddess S + Peeing Boy x 4 = Red glow in room, Peeing Boys all turn to face the wall
Dragon S + Knight x 4 = Red glow, Knight statues face the Dragon S with swords raised