In Fire Emblem Fates, Guard Stance (防陣, Bōjin lit. Defense Formation) is a game mechanic that works similar to Dual Guard in Fire Emblem Awakening. If two units are paired up, the main unit gains stat boosts dependent on the secondary unit's current class (e.g. a Berserker will primarily give strength/speed, while General gives strength/defense) and the two units' support level. Supported units that pair up together increase their boosts. Like Attack Stance, enemies can also use Guard Stance, but cannot actually perform this in-game; any enemies using Guard Stance are always paired up prior to the start of the battle.
In Guard Stance, dual attacks from enemies in Attack Stance will always be blocked. The supporting unit in Guard Stance will be unable to attack unless the Bold Stance skill is equipped. The skill Nohrian Trust allows the lead unit to use skills from the supporting partner.
Unlike in Awakening, where the guard chance is based on the skill Dual Guard and Support level, guard chance is always the same regardless of the paired units. Once paired up, the pair will share their shield gauge, which initially starts at 0, and has 10 increments. Each attack (by attacker or defender) not blocked by Guard Stance will increase the gauge by 2, even if the attack misses. Activating multi-hit skills Aether and Astra will give two Dual Guard points per hit. The gauge decreases by 1 every turn if the pair does not attack and is not attacked by the enemy. Once the gauge is completely filled up, the next attack will always be blocked, regardless of hit chance. Blocking an attack that reduces stats (Daggers or weapons like Setsuna's Yumi) will negate the stat reductions as well.