Enemies: Gaia Snake, Gaia Ape, Gaia Horn, Gaia Demon, Gaia Fly, Gaia Scorpion, Gaia Bird
As Liete says, the monsters have been affected by Gaia, so that means that they’ve gotten harder. This goes for the Savanna Wilderness too (not the Brinan Plateau for some reason), so now would be a great time to level up if you want to. Just go back and forth between those two areas. The Gaia Horns can replicate just like their earlier forms, and are amazing to grind range / all magic against.
Follow the path as it turns south and go through the door. Continue southeast, past the stairs to the northeast, and up the ones to the four-way fork. Head north-northeast and follow the path, past the spinning Apes, all the way to a fork. Go south and up the stairs, past some jumping Apes, down some more stairs, and east-northeast at the next fork to the East Luzet Mountains.
There’ll be an earthquake, and then you’ll see J Base preparing for a defense. A soldier will report that Leen went to one of the turrets, and Mullen realizes that she’s going to try to fight it alone.
Back at the Luzets, use the Save Point if you want, then head east and north. At the next fork, go southwest, then west down the stairs. Head northeast and go all the way to the other side of the tunnel. Go south, then southeast up the stairs, then go south, and follow the path and the spinning arrow to the exit.
Once you enter J Base, you trigger the events to go forward with the final dungeons of the game.