Capturing is a game mechanic that allows you to capture an enemy unit and imprison them so you can bribe or persuade them to join your army. There are only two characters who can use this command: Orochi (Hoshido) or Niles (Nohr). For Niles, the command is "Kidnap".
Orochi
Niles (image courtesy of FE Wikia)
When capturing, you need to consider the following pointers:
- The Capture Command is selected from the character's action menu. This will make him/her initiate a capture attack. (normal attack but with lower accuracy) That attack should be the finishing blow in order to successfully capture the target. Upon capture, you'll see a confirmation.
- Requires Prison to be built first in your castle.
- Your prison should have available space to accommodate your prisoner. If it's full, you can't capture additional characters. You can persuade them to join your party or release them.
- The targeted enemy should be capturable. Faceless, Invaders, story bosses, and playable characters (belonging to another faction) usually can't be captured.
- The Capture command is retained even if you re-class Orochi or Niles