|Astral Sea||Defeat the boss.|
This paralogue allows you to recruit Shigure, the son of Azura. You will start out in his Deeprealm, which is being attacked by mysterious Invaders. The battleground takes the form of three ships, one of which is yours. However, what makes this stage special is that the boats are continuously moving every single turn. So on one turn, the top ship will "broadside" (i.e. crash into) yours, while the bottom ship is far away.
Keep your units centralized, or if you do send them out to the other ships, do so in sizeable packs. Nothing is worse than having one or two units be isolated by the ships as they move, and then having them be ruthlessly crushed by the enemies. Any sort of flying unit will shine here, since they can freely navigate independently of the ships' movements. However, as if foreseeing such utility, the boats are absolutely jam-packed with archers. It's recommended you use Sky Knights as a way to ferry your more durable units around, as opposed to giving them the spotlight in combat, where they can be shot down.
Reinforcements will be arriving almost every turn, so defeat the boss whenever you feel comfortable and Shigure will permanently join your army.