While in the Sepulcher, your party gets split up. Astra, Hiante, and Relenia don't do well against the enemies that are about, and Snowe and Erio are so outmatched that they have to do a Stealth-Based Mission. And then you get everyone back together, and with all five of them present, enemies that you were probably bravely running away from are suddenly easy to take down. Awesome.
Everything about the final boss fight, from the music to the imagery to the fact that Richard, Erio, and even the town's children all show up to help you at various points (the children even poke a hole in the boss's defense!), and given how many hitpoints the guy has, the moment you finally defeat him is very satisfying indeed.
In "A Demon", when Erio enters Astra's dream to try to stop her nightmares, the first thing he has Astra do is dream up a door, and he defends her from the very angry flames the whole time. The door unfortunately shows up on the opposite side of the room from where they need it to be. So Erio rotates the walls.