Loosely, affinity determines a character's stat boosts that are gained from supports. Supports depend on the affinities of the two characters that are being bonded, and they determine the type of bonus given. The following tables are a compilation of bonuses given by the dark affinity in each game.
The Dark affinity is a rarity in the Fire Emblem series, as only a few characters possess it in each game. It gives neither offensive nor defensive bonuses in the GBA games, making it somewhat of an oddity, as it gives full Hit, Evade, and Critical instead. In the Tellius series it became an offensive affinity.
Dark Affinity Bonuses in Fire Emblem: Fūin no Tsurugi
Dark Affinity Bonuses in Fire Emblem: Path of Radiance
