The objective of this map is to defeat the boss. There are also several chests that can be looted so bring at least two characters with Locktouch in this battle since there are no enemies who will drop chest keys upon defeat. You'll have to divide your forces again since you have to activate the dragon veins to freeze the water and stop the reinforcements from appearing from the pools of water. However, take note that the ice will eventually melt so keep an eye for them when this happens. Once the ice melts, the dragon vein needed to freeze it will appear as well.
After Azura and the avatar ends their turns, a 3x3 ward will activate around them, providing additional protection and automatic healing to allies within range. That said, you can assign a few of your powerful units to go along with your avatar and use him/her to take on the central path and get the aggro of all the enemies there. For the meantime, you can assign Azura to one of the smaller groups who will attempt to loot the chests and freeze the pools of water on each side of the map
During the first turn, freeze the water near your starting point. It will take a while before the ice melts, probably about 6 turns. Gunter's range is about two spaces around him and he won't move around to attack your forces. Once you've looted all the chests and cleared most of the enemies, head towards Gunter and finish him off to complete the chapter.
Chest Contents:
NE: Nosferatu
Middle, NE: Crescent Bow
Middle East 1: Beaststone+
Middle East 2: Fortify
SE: Rescue
NW: Brave Sword
Middle, NW: Calamity Gate
Middle West1: Brave Axe
Middle West2: Brave Lance
SW: Blessed Bow