Enemy Tips : It seems the imperials have driven off the local wildlife... The Desert Snipers use Desert Camo to trigger Utsusemi for one turn. If you hit them during this state, they will retaliate with Counter. Desert Katanas prefer to use Mincemeat to deal three hits to one character.
Meanwhile, Desert Spears use Execution to deal big damage to one. Finally, Desert Blades are meanies who use Prey on the Weak to damage the character with the lowest HP. Drench the snipers with water and zap the rest with lightning.
Upon arrival at the Harena Sea Caves, you'll discover that all of the dungeon traps have reverted to their original positions. You did travel back in time after all! To save repeating ourselves, if you need help, please refer to the Harena Sea Caves section in Chapter 1 of our guide.
By the way, this unfortunately does not extend to the treasure chests. Those have a magical memory that can transcend space and time, just like our heroes... Anyway, once you reach the compass within the Depths, prepare for another bloody battle with Geist... and son.
Boss: Geist and Revenant
At the start, father and son do nothing except use standard physical attacks and Undo HP. Begin by buffing your party's physical defence with a Performer or other means and focus everything on Geist. Thankfully, the Exorcist is much more frail than in his solo battle.
Like before, physical attacks are best since Geist has high magic defence. To really hammer the pain, use the Doujigiri-Yasutsuna from the Geyser Grotto locked chest to deal effective damage to him and his son. If you have time, buff your party's physical attack as well.
If you combine all of this with the techniques of a Fencer, you can even finish Geist in two rounds of attacks. However be careful as Revenant will eventually use Soul Mirror on his father, which reflects physical hits.
When this happens, use the Exorcist's Purgation to remove it. Otherwise, you've little choice but to switch targets. In addition, remove Stampede or any ability that will trigger a counter-attack because the counter-attack will be reflected on you.
Meanwhile, Revenant has high physical and magical defences, but you can take advatange of his weakness to the light element by using the Hawkeye's Shininghead or similar means. The Doujigiri-Yasutsuna will also put a big dent in his armour.
Watch out as each time you damage Revenant, his Soul Power will build up. After suffering five attacks, his Soul Power will rise to 100%. Should this happen, he'll use Soul Blaster to damage the party. Default to brace for the attack or use Undo Action to avoid it altogether.
Finally, after Revenant goes below half HP, he will use his notorious Possession move to take control of one of your characters. Quickly boot Revenant out by carefully attacking your possessed party member, then use Undo HP on Revenant to OHKO him.
Beware that Revenant is pretty fast, so give your Exorcist the Hermes Sandals for a better chance of outspeeding the clunking Guardian. If Revenant possesses a character who's somehow too bulky to damage (like a Performer with max buffs), use the Hawkeye's Harpoon.
Alternatively, you can whittle Revenant down to almost half health, then unleash an onslaught of attacks to finish him off in one turn. You'd be surprised at how effective the Doujigiri-Yasutsuna, Shininghead and physical attack buffs can be.
By the way, if you defeat Revenant first, Geist will occasionally use Mercy Killing, which has a 1/3 chance of instantly KOing each party member. You can avoid this with Undo Action, but it's probably safer to defeat Geist first.