Follow-Up Attack (追撃判定, Tsuiseki Hantei) is a core combat mechanic that has existed throughout the Fire Emblem series since its inception, though it was only recently named.
Prior to the official naming of this mechanic in Fire Emblem Fates and the mobile game Fire Emblem Heroes, the mechanic is often referred to by fans as a Double Attack.
Overall[]
A Follow-Up Attack refers to the inherent ability for a character to perform multiple attacks against a foe in a single round of combat. The primary determining factor in this is the inherent differences between the two units Speed stat. The threshold of Speed difference between games varies, though generally a Speed difference is anywhere from 3 to 5. Whichever unit has the higher Spd stat and fulfills the game's Spd threshold gains this ability.
When a Follow-Up Attack is possible, it is usually noted on the Combat Forecast with that unit's damage stat showing a "x2" next to it. Combat attack flow differs slightly depending on which unit attacks first when a Follow-Up Attack is possible. If the unit with the Follow-Up Attack initiates combat, the unit will attack first, allow the foe to counterattack if possible, then the unit performs the follow-up attack. If the foe initiates combat, the foe will attack first, then the unit performs both attacks consecutively.
In games that feature a weight system for weapons, this weight can offset the character's ability to perform Follow-Up Attacks despite the natural Speed stat advantages as the character needs to meet certain Constitution or Strength stats thresholds to offset the Weight penalties.
Follow-Up Attacks are considered wholly separate combat mechanics and can stack with certain skills or weapons, such as Adept or Brave weapons, to unleash more attacks. Some skills, like Wary Fighter or Null Follow-Up, also help or hamper the ability to use this mechanic as well.
Mechanics by Game[]
Follow-Up Attacks have a unique effect in Fire Emblem: Thracia 776, where the Pursuit Critical Coefficient differentiates the user's critical rate for the first and second hit from Follow-Up Attacks.
In most games up to Fire Emblem: New Mystery of the Emblem and in Fire Emblem: Three Houses, Follow-Up occur when the attacker has an attack speed of at least 4 more than their opponent.
In Fire Emblem Gaiden and Fire Emblem: Genealogy of the Holy War, Follow-Up Attacks occur when the attacker has higher attack speed than their opponent. In Genealogy of the Holy War, characters must possess the Pursuit skill to be able to double attack.
In Fire Emblem: Mystery of the Emblem, Follow-Up Attacks occur when the attacker has an attack speed of at least 3 more than their opponent.
In Fire Emblem Awakening and Fire Emblem Fates, Follow-Up Attacks occur when the attacker has at least 5 points more speed than their opponent.
In Fire Emblem Fates, certain weapons can affect double attack thresholds. For example, Steel weapons make it harder to perform a Follow-Up Attack (requiring 8 more speed), Effie's Lance makes it easier for the enemy to perform Follow-Up Attacks (requiring equal speed) and so on. In certain circumstances it is even possible for both characters to perform Follow-Up Attacks at the same time (for example if a character uses a Chakram to attack an enemy with equal speed). The skill Wary Fighter negates the double attack mechanic in battles involving a character equipped with this skill.
In Fire Emblem Heroes, Follow-Up Attacks occur if the character with the higher Speed has at least 5 points more than their opponents. Several skills and weapons affect the ability to Follow-Up Attacks such as Wary Fighter or Null Follow-Up.
In Fire Emblem Engage, Smash Weapons cannot perform Follow-Up attacks.