Near the Xantezza altar, use Spirit Vision to spot the ghost of the Knight Of Xantezza. Talk to it to learn that Imp Gen has been stolen.
If you decide to help, you will have to get near the Lunar Gate. To wolves will be guarding Large Ruby. Get rid of them by offering them any limb from your inventory or just killing them.
Then talk to Large Ruby. You will want somebody, who's a mystic to do that. It will allow dialogue options, which guarantee a successful outcome of the conversation. After calming Large Ruby you will be taken to some sort of clockwork. From now on, you will move in slow mo. The task is to escape the core.
There are two ways. The first one goes down the pipeline that begins right next to the fast travel point.
Teleport your team and go to the end of the path. Thence you can teleport your team member right next to the core.
The other way takes you through the room next door. It is, however, much more difficult. You will need to open the door in the first room. In order to do that, all four switches are pushed down. Use crates to achieve that. You can also use three characters and one crate.
If one character can go through, it will be able to teleport the rest. You will get into a room wit traps that create a poisonous circle.
There are another door there, which lead directly into the core. Reaching there from this side is only possible if you teleport a character with the Spread Your Wings ability as close to the core, so that it's able to fly to it.
When the core is stabilized, the quest ends.
Reward: 20075 experience points + 4 guaranteed rewards + 1 z 3 to choose from depending on character class