This mission starts with a Moogle Thief being harassed by a judge about whether he's harboring the kid with the bounty on his head. Marche storms in and yells at the judge to leave to innocent Moogle alone and free any other prisoners they've taken for questioning, saying that he will turn himself in.
A battle ensues, featuring a Sage, two Mog Knights, two Templars, a Paladin, and a Gunner. The Paladin has some highly damaging attacks, and he has the Drop Weapon ability to disarm your allies, so he should be one of your top priorities. The Templars are also pretty tough, so defeat them early on if you can. You should try to use ranged attacks against them, because they have Bonecrusher, which is like Counter, except the Templar that you hit will deal you twice the damage that you inflicted upon it. It might also be a good idea to inflict status ailments on the Gunner to reduce its ability to hurt you, because it has such a huge attack range.
Once you complete that battle, Judgemaster Cid comes along and takes you to the Sprohm prison to question you. Babus enters and confirms that you are Marche. Marche then demands that Cid release the other clan members, but Cid refuses, because they aided a known criminal. Cid and Babus chastise Marche for wanting to disrupt Mewt's world, but Marche tries to explain that this is a world that Mewt created so that he could avoid his problems in the real world--a dream world. To Marche's surprise, Babus claims that Mewt has said that if this world must end, Mewt would rather destroy it himself.
Suddenly, a seam opens up in the interrogation room, much to Cid's shock. Babus claims that Marche somehow called the seam into existence there. The group finds itself in a temple-like room, as with the other crystal rooms. The crystal is encased in a structure of tree roots, and there are Exodus Fruits all around.
Marche expresses his determination to destroy this crystal, but Cid warns that because Marche's clan is locked away, he must fight by himself. Marche is very nervous, but he still wants to try to destroy the crystal.
This battle is between just Marche and Babus, with Cid enforcing the laws. The goal is to destroy all of the Exodus Fruits, which have no attacks, but don't bother trying until Babus is dealt with. He is a formidable foe. It will help if you have items equipped that confer defensive status changes, particularly Auto-Life, Auto-Regen, Mirror, and so on. If Babus has a higher speed than you do, then he will get a chance to do something very damaging to you right at the start of the battle, so having something like Auto-Life will help you have a fighting chance. Otherwise, you need to have some highly damaging attacks of your own to quickly wear down Babus's hit points. Once Babus has been KOed, go around the room killing the Exodus Fruits. They won't do anything to you, and Cid will just sit there--unless you break a law, of course. To win this battle, I had Marche be a Ninja with Nosada equipped so that he could use Double Sword, and had the other sword be the one from my inventory that granted the biggest increase in Weapon Attack. I was lucky, and one of the sword hits was a critical hit, so I KOed Babus in one turn.
With the battle over, Babus recovers from being KOed, and the crystal disappears. Then, the version of Cid and Mewt from the real world appear, and Cid apologizes the way that he was in the opening scenes, with Mewt commenting on how Cid fell apart when Mewt's Mom died, as he did at the beginning of the game. Then the real-world Cid and Mewt disappear, and Cid expresses disbelief at first. But when the three are returned to the Sprohm prison, Cid admits that after seeing the version of himself from the real world, he remembers his life from the real world. He declares that he will separate himself and his judges from the palace, overseeing the law independently of Prince Mewt.