Use the NightShade rage and wait until Gau/Gogo uses Charm. When Charm is cast, NO enemy in the game has a defense from it. Even the final Boss. Most likely an overlook by the developers - they didn't expect you to be able to use Charm in the first place, or rather they forgot about it. Since there is no programming or monsters, it will use the Character's code to hit themselves. But a monster's Vigor and Stamina are random and chosen at the beginning of battle, while a Character's are not. In this way, Charm's resistance is thrown off-balance, and it goes a bit haywire. The monster will attack itself until it dies. Even if hit with a physical attack it won't turn back to normal. If you want to have a fair fight, you must kill your Charmer and the battle will return to normal.
Submitted by: Thor