“A feather that increases speed by 2.” —In-game description, New Mystery of the Emblem
The Speedwing (高速翼 Kōsoku tsubasa) is a Stat booster that recurs across the Fire Emblem Series. Prior to Fire Emblem: The Binding Blade, the Speedwing's original form is the Speed Ring (スピードリング Supīdo ringu). When used, the Speedwing permanently raises its user's Speed by a set number of points that varies from game to game.
While speedwings can be used to give fast units even higher evasion stats or patch up the Speed stat of an otherwise slow unit, Speedwings' true value lies in their ability to allow units with middling or slightly above average speed stats to double opponents they would otherwise not be able to double. If used to push a unit over the statistical threshold necessary to double an important enemy class or boss, they can massively shape the outcome of battle, turning otherwise insurmountable charges into a manageable threat.