Resonant Battles are a unique Arena game mode for Fire Emblem Heroes.
Players deploy a standard teams of up to four characters from their roster to stop thieves from escaping a map with valuable loot. For their protection, powerful Heroes are deployed on their side to impede the players. As an extra challenge, the player is only allowed to deploy characters from two specific Fire Emblem titles that are highlighted and rotated each week. Originally the player was only given nine attempts at completing the map at the beginning of the mode's existance, but these limited attempts were later removed.
After building a team of up to four characters, the player starts off on the south end of a map and must quickly dispatch as many enemy thieves as possible. The thieves quickly make their way to the northern most points of the map highlighted in yellow. If any thief reaches that point, they escape the map. A battle ends if once there are no thieves left on the map, either if the player defeats them or if they escape. Thieves do not carry weapons, thus cannot attack or counterattack but their stats scale to the player's rank and the current difficulty chosen. Additionally, Thieves have their movement reduced to 1. Upon defeating a thief, they will drop a consumable item like the ones found in Arena Assault and the player can use these items to help clear the map. These items include the Lightning Charm, Infantry Boots, Elixir, Dancer's Veil, Special Blade, and Fortifying Horn. The item dropped by a thief is fixed on the same map.
To add difficulty, the thieves are protected by powerful Heroes whose power scales to the player's rank and difficulty chosen. In exchange, the enemy Heroes have limited movement, reduced down by 1 for the normal movement range they would normally have, but retain the normal range of their weapons. Enemy Heroes do not move from their starting points unless a player's Hero moves into it. Players may defeat them, but there are no rewards for taking down an enemy Hero.
Players are scored based on the difficulty chosen, the number of enemy thieves defeated, and how many of the player units are still alive at the end of a battle. The player can earn additional points if they deploy a Resonant Hero. Players are not rewarded for defeating any enemy Heroes.
At the end of a week, the player's Resonant Battle score is compared to other Heroes players in the same tier. Players can change rank depending on their ending score up to the highest rank of 21. Players earn rewards based on their ranking.