Castle Battles
You have the option to battle other players in an attempt to seize their throne. If you successfully seized the throne, you can either recruit any one ally from the castle lord’s army (even the castle lord’s main character) or get any non-unique skill at a discounted cost. There will be castles with deliberately undefended thrones to entice other players to visit them. These castles may also have easily defeated units where you can acquire new skills for your characters. Take note that a character can only learn skills from another character of the same name. For example, your Azura can't learn the skill Hoshidan Unity from another player's Corrin.
Deeprealm Invasions
There will be times that your castle may come under siege, either by other players or game NPCs called “Invaders”. You can bring up to 10 units (will still depend on the type of invasion) to defend the throne room and Lilith will act as an independent unit. You can still move buildings using the Edit command and buildings destroyed in the battle will be repaired afterward.
The attackers will arrive from all entrances of the castle. You can place them strategically near the throne or in front of your buildings. Since your units will be probably placed separately, you can have them fall back near your position so they can support each other.
The invaders will not just attack your units; they’ll also attack your buildings. Don’t worry however, destroyed buildings will be repaired automatically after the battle is over without extra cost. While your buildings may appear as efficient distractions to the enemies, some of them provide stat bonuses to your units during a castle defense session. Losing these stat-boosting buildings will immediately remove the stat boosts they provide.