Capture (捕捉) is a recurring gameplay feature that appears in Fire Emblem: Thracia 776, to an extent in Fire Emblem: Radiant Dawn and in Fire Emblem: Fates. Under certain conditions, characters can capture those from the opposing side, equivalent to rescuing allies.
Thracia 776
Characters can only capture enemies that have a smaller Build compared to them, though mounted units are exempt from this rule except while dismounted. When a battle is initiated with the intention of capture, the character's Strength, Magic, Skill, Speed and Defense are all halved, so it is advised to weaken the enemy prior to a capture attempt, unless the character is powerful enough to inflict sufficient damage regardless of stat reductions.
The enemy's HP must drop to zero in order for the capture to take effect. Brave weapons like Finn's Hero Lance or the skill Charge are considered very helpful in a capture attempt.
Once an enemy is successfully captured, the character can trade with their hostage to take anything in their inventory. They may also release the hostage, although this counts as killing them gameplay-wise (whereas just holding onto them until the chapter's end counts as if they have never been fought). Ostensibly, releasing a captured unit counts as letting them escape the battlefield with their lives intact, in relation to the story.
Capture is an extremely important element in Thracia 776, especially since the game begins with no gold and selling stolen weapons is almost required to earn funds, unless the player exploits the arenas available.
Certain characters can only be recruited by first capturing them, and then finishing the chapter without releasing them. These characters include Lifis, Salem, Trewd, and Misha.
Mounted or airborne units cannot be captured normally, unless they have been put to Sleep, in which case they are treated as though they have dismounted. Characters with a Build of twenty cannot be captured, though. Interestingly, unique enemies and bosses usually say different lines if they are captured and released, instead of merely defeated in combat.
Enemies may also attempt to capture the player's units, so keeping non-combative units, such as Priests, away from the front line is strongly recommended at all times. Any unit that is unarmed will always be captured in an attempt, as they have no means to defend themselves. It should be noted that if a unit is captured, the enemy is severely weakened, making them very easy to defeat and get your unit back; therefore, sometimes putting an unarmed unit in the front lines can be useful for defeating more difficult enemies.
Radiant Dawn
In Fire Emblem: Radiant Dawn, a very similar mechanic exists, though it only appears in the Prologue of Part II; in this chapter, the opposing Begnion Dracoknights will capture Princess Leanne if she is within their range.
Fates
In Fire Emblem: Fates, the ability to Capture is only available to those who either have the Hoshidan Capture or Nohrian Restraint Skill. A Jail must also be available in My Castle to utilize this feature. Once an enemy is defeated by a unit with the Capture command, they are placed in the Jail. Players may spend resources to convince these jailed units to join or can send an army member to convince them for a lower resource cost. Players cannot capture characters exclusive to the opposite route they are playing, though some unique bosses can be captured and recruited.
Captured units can be used like normal units, however they cannot form supports with any other units.