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.
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!