If unit's Def > foe's Def, reduces damage from attacks during combat and from area-of-effect Specials (excluding Røkkr area-of-effect Specials) by percentage=difference between stats × 4 (max 40%), and also if foe initiates combat, unit makes a guaranteed follow-up attack.
This skill can only be equipped by its original unit.
For example, if both Spurn 3 and Vital Astra activate, the maximum total damage-reduction is 58% instead of 70%, since the two skills reduce the damage to (1 − 40%) × (1 − 30%) = 42% of the original damage.
Adroit War Tome and Þjálfi can reduce the damage-reduction of Blue Lion Rule by 50%.
As a general rule, if a unit is both prevented from making, and guaranteed to make, a follow-up attack, the effects cancel out, and the standard speed check decides instead.
A foe with skills such as Null Follow-Up 3 or a status effect such as Null Follow-Up will disable Blue Lion Rule's guaranteed follow-up attack effect.
Wo Dao+.
Deadeye, 
