This is a large map with only two dragon vein points near the entrance and another one right under where the gate guardians are standing. When activated, they will cause a landslide inside the castle that can 10 points of damage all enemies per vein.
The main boss of the map is the strategist Daniela which you can Capture using Orochi. If you want to expand your army or have a unique, side character in your army, you should bring Orochi in this battle and attempt to capture her. At the gate of the castle, you'll have to deal with the pair of Benny and Charlotte.
Make your preparations and remember to split your healers in at least two groups. For the first turn, end your turn immediately to force the outlying enemy troops to come at you. This will allow you to pick them off with an initiated attack. Be careful since the enemy Paladins have great range, defense, and damage. Your troops might get decimated if you're not careful. On the 4th turn, several units will appear inside the castle as reinforcements. They won't leave their positions so concentrate on clearing the courtyard of enemies.
Once done, make your way in the middle and converge your troops so you can assault the guardian of the gate. As long as you stay away from Benny and Charlotte's attack range, you can place your units around them and prepare for an assault. It's recommended to whittle down his HP using ranged attacks; if your characters are already powerful enough, just go and take him head-on.
After defeating Benny, activate the dragon vein on his original position. Take note that the enemies inside the castle will not engage you as long as you stay away from their attack range. Get your troops positioned near the gate and prepare to storm the entrance, preferably with the royal family members first so they can trigger the veins before entering Combat. If you're able to activate three veins in a single turn, that will cause a total of 30 damage to all enemies inside, giving you one-hit kills since they don't have healers among them. Getting rid of the remaining forces including the boss should be easy already at this point.