This was once a fortress to protect the land but now it's the monsters base. Capture the fort back!
Citadel Battle is the tenth main Story Mission. This is quite a challenging mission, and may be an obstacle for new players. Much of this is due to the Baphomet boss with his large HP pool and highly damaging attacks. The Heavy Infantry enemy (previously featured in the skippable Gate Defense mission) is also no slouch.
This stage introduces the enemy Baphomet, while you had to deal with a more powerful one in Cloris' Urgent Mission Drill (Witch Feast) this one is not as powerful and shouldn't give you as much trouble compared to that one, don't use a ranged units skill until the end so you can bombard the final enemy rush.
Place Katie on the upper spot of the intersection near the HQ (spot D), then place Bashira on the center lower area of the upper grass area (spot T) to help deal with the Goblin Soldiers. Place Phyllis on the spot below Katie (spot I). Katie's skill should be ready so use it and bring Soma on spot W on the map. Wait until you have enough UP to place Valerie above Bashira (spot Q). Phyllis' skill should be ready so use it and bring Mortimer on the spot above Katie (spot A). Katie should have her skill ready again use it and bring Iris on the ranged spot closest to the melee units on the upper grass are (spot S). Phyllis' skill should be ready again so place Cloris on the spot closest to the upper camp exit (spot R). When you have the UP place Roy on the spot closest to Phyllis (spot V) and a Heavy Infantry should be coming around to Mortimer activate his skill. Withdraw Mortimer after the Heavy Infantry has been defeated and place Leeanne in front of Katie (spot E). Withdraw Phyllis place the Prince in her spot before the Ogre and Archer reach it. Place Alissa on the spot under Soma (spot Z) to delay the Archer from reaching the Prince while the Ogre moves in his direction.
When you see the Baphomet appear from the center camp exit activate everyone's skill except Bashira's until the enemies are in her range, when the Baphomet reaches Leeanne her skill should be ready so use that to keep her alive while she is blocking it. Max unit capacity will increase by 4 after finishing this stage.
3★ with level 1 units, Prince level 22
Before the sortie, make sure the Prince is set to the best "Skill Effect" Title available. (Descendant of the Hero is fine.)