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 thunder affinity in each game.
The Thunder affinity grants defensive combat bonuses, and is usually beneficial for support units, such as Clerics and Troubadours, or units with low durability that are reliant on their evasion to survive. Because it also gives a boost to Critical hit rate, Thunder can be a desirous affinity for myrmidons and swordmasters, as it increases their characteristically high critical rate as well as their low defense.
Thunder Affinity Bonuses in Fire Emblem: Binding Blade
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