You can access the Astral Caves as an optional Quest after performing an "Ogre Battling" quest for Lias. Here you join the Astral Knights on a mission to defeat the monster inside causing earthquates to the area.
Roddick and his friends persuit Phia's look-alike, who had attacked Lias on the same night. Upon reaching the Tatroi exit, the party faces the lookalike, who is actually an assassin Darthwidow sent by Asmodeus himself.
Character Recruitment Changes
In case the player hasn't recruited Ashlay, Phia will temporarily join the party in this dungeon.
Star Ocean: Fantastic Space Odyssey/First Departure