Go to Cadoan and you'll see some people complaining about the laws and the Queen. Then a Nu Mou tells them of Ezel Berbier, a mysterious individual who has discovered a way around the laws.
The next time you go to Cadoan, you'll see that same Nu Mou from before being chased by the people he had been talking to before about Ezel Berbier. It turns out that that Nu Mou is none other than Ezel Berbier himself, and the group is chasing him because they feel that he is overcharging them.
Ezel is an Illusionist and his ability is to put all enemies on the screen to sleep. He will also use the fight ability. Don't let Ezel get KOed because that will make you fail the mission. You can't control him, but you can heal him if he needs it.
How you prioritize this battle depends on who you have in your party. When you choose your units, consider the fact that most of the enemies are stronger physically than magically, with the exception of the illusionist. You should probably choose units that have high weapon defense, and fairly good magic defense. Having units with strong ranged attacks will also serve you well. Aside from that, your decision of how to prioritize this battle depends on which enemies are hurting you the most.
After you win the battle, Judgemaster Cid arrives on the scene. Ezel is not willing to go to prison, so Cid is forced to use an Advanced Law to stop Ezel in his tracks. But Ezel whips out an Antilaw and disappears. Cid gives up and leaves the scene.
Marche and Ezel talk in the Cadoan pub. Ezel explains that law cards can modify the laws of the day, removing laws and adding them. He offers to trade law cards with Marche in his Cadoan shop. Trading consists of giving up some of your own cards in exchange for the ones he has. Each card has a point value, and you have to give up enough cards to match the point value of the card that you want.