You’ll only have Azura and Felicia in your group. To win this mission, you have to defeat both commanders of the two armies. You can use Azura’s Sing ability to help you take a turn twice and with Felicia as your healer and ranged fighter. You can’t afford to pair up units at the moment so head out and attack the Hoshidan side first. The Nohrian army fliers will also attack you. If you’re playing in classic mode, make sure that Azura is out of their range since she’s too weak to survive two consecutive attacks. After defeating the two commanders, the mission will be over.
After the battle, Lilith will take you to the Astral Plane where you have to maintain your own castle. (Note: If you have another castle from your previous route, it will still be your castle until you update new castle data. Castles from each route saved separately)