*** Spoilers ***
Taken Directly from Mike's RPG Center
If you choose Judge Fairweather from the Bracada Desert, he will find a way to resolve the dispute between the humans and elves. You will be asked to speak with Gavin Magnus in Celeste.
Go to the Bracada Desert and step on the teleporter near the center of the area to go to Celeste.
Enter Castle Lambent and speak to Gavin Magnus. He will ask that you first complete the Walls of Mist.
Enter the Walls of Mist near the south end of Celeste. Since you are not allowed to kill any of the enemies inside, it would be much easier for you to cast invisibility before you enter so that you can avoid the enemies all together.
In the main room there are three arches in the center and three pillars at the back. Pass through each of the arches to find a key for each of the pillars.
In the area through the west arch, there are three buttons and a lever on both the west and east sides of the area. Press both of the center buttons and then pull one of the levers to reveal the chest holding the West Pillar Key.
In the area through the central arch, step up to the wall in the southwest corner of the room and the floor will rise to bring to the room where the Central Pillar Key can be found. Step on the same floor tile again to descend.
In the area through the east arch, head straight north and walk through the curtain. Press the button to use the lift. Press the button on each of the four pools to drain the water from the pool at the back of the room and jump into the hole there to reach the room with the East Pillar Key.
Return to the main room and click on all three pillars to open the path to the exit.
Speak to Gavin Magnus again and he will congratulate you on your success. He will also ask you to speak to his advisors.
Go to the east end of Celeste and speak to all four advisors. Three of them will have quests for you.