This battle plays like a cross between the volcano hole and save Irene battles from Scenario I - you're underground in a cave, and there's a female character, Hazuki, who needs saving. That should all seem straightforward enough.

Initially, Hazuki is computer-controlled, which means she might not always make the best decisions. With this in mind, you should try and get somebody to her as quickly as possible, preferably Campbell. The Worms in the top left of the map and the Scaven in the bottom left don't appear until you start moving, so avoid getting ambushed by keeping Rock or Medion near the back of the pack, to fight them off. They don't keep re-appearing though, so it shouldn't be too much of a problem.

Hazuki's quite fast, and thankfully the enemies only attack her one at a time, so Campbell should reach her in three or four turns. Stand next to her and choose talk, then answer yes to get her to join your squad. She's now under your control, and your first move is likely to be to get her healed, but you'll need to get someone else to do that because she only has a shuriken on her. When she's in your squad, the Succubus boss will appear, but don't go for her just yet.

Take down the rest of the enemies and send someone to pick up the Large Mithril (inspect the pillar), and likewise to get the Lucky Cookie held in the treasure chest. Now, the rest of the enemies should have been dealt with, so regroup and concentrate on the Succubus.

If you're using a Scenario I save file and you have Barnard, he'll be a great help, but if not then you can still win the day by using Medion and Campbell for hand-to-hand fighting, with Syntesis using Blaze and Waltz contributing with her arrows. With this winning combination, you should save the day.

Note: If you talk to Hazuki and she then dies, as long as you finish the battle she'll remain a member of your squad. Just make sure you get to her before she cops it!

Newts