I couldn't miss the chance to practice my drawing!

Iainuki in Final Fantasy V.
Knocks Out the target.
Iainuki (いあいぬき or 居合抜き, Iainuki?), also known as Iai Blow, Iai Strike, Slash, Fdraw, Flash or Iai, is a recurring command ability in the Final Fantasy series that has also appeared as an enemy attack. It typically attempts to instantly kill the target. The job class Samurai is most often associated with the technique.
Sephiroth from Final Fantasy VII has an attack called Sudden Cruelty that has a similar name in Japanese: Iai Strike.
Appearances
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Final Fantasy V
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Unleash an attack that hits all enemies in an instant.
Iainuki is the Level 5 ability of the Samurai, learned for 540 ABP. It usually has a 85% chance to instantly kill all enemies, but takes into account the level factor all magic attacks use and will never work on Heavy targets.
Final Fantasy VII
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Flash (Iainuki in Japanese) is the final ability of the Slash-All Command Materia found in the Ancient Forest. It allows the user to attack all enemies and attempt to inflict instant death. The chance for Flash to hit an enemy is equal to the equipped weapon's Atk% halved. Flash has the opposite effect to undead enemies, causing full recovery.
Final Fantasy VIII
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Iai Blow is an enemy ability used by Forbidden when it has less than 85% of its HP remaining. It does physical damage and has a chance to instantly kill the target.
Final Fantasy IX
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Iai Strike is a Sword Art for Steiner that attempts to instantly kill an enemy with 30% accuracy. It is learned by equipping a Rune Blade. Iai Strike can be missed altogether because the Rune Blade can only be bought in Daguerreo before entering the Shimmering Island.
Final Fantasy XI
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Iainuki is a special Weapon Skill used by the Bastokan NPC, Kurt, during the Shadow Reign era. It inflicts damage in a frontal cone and causes a knockback effect on all enemies hit. Its Skillchain property is Detonation, a level 1 Wind skillchain.
Final Fantasy XIV
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Final Fantasy Tactics A2: Grimoire of the Rift
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Iai Blow is part of the Flair skillset used by the Parivir class. It attacks a target for damage equal to half a normal attack with a chance to kill them instantly equal to that unit's critical hit rate. It is learned from the Osafune and requires 300 AP to master.
Final Fantasy Tactics S
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Final Fantasy Dimensions
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Deals damage and instantly kills a single enemy.
Iai is a Fusion Ability unique to the Warriors of Darkness that combines the Dark Knight's Final Thrust attack with the Summoner's Odin. The warrior singles out a target, and delivers a swift attack that buffets the foe with shockwaves. It deals damage and has a chance to instantly kill by slicing the foe into pieces.
Final Fantasy Dimensions II
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The Ninja Jinnai is seen using Flash several times, which has a similar effect of slicing the target apart. However, the player cannot command Jinnai to use this attack in battle, and it is not an ability the player can gain by using the Ninja class.
Dissidia Final Fantasy (2008)
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You look good.
Iai Strike is an ability connected to the Smiting Soul accessory. Iai Strike gives the user a 2% chance to inflict an instant Break on the opponent whenever they damage their Bravery.
Iainuki is the ability of the Samurai card in the Duel Colosseum. When used, the Samurai card discards all Chaos and Boss cards in the hand.
Dissidia 012 Final Fantasy
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The Smiting Soul accessory returns. Iai Strike is the name of the effect tied to the Zantetsuken wielded by Gilgamesh, which has a random chance to instantly inflict Break when Gilgamesh randomly uses the Zantetsuken to attack.
Certain accessories also have a related Assist Iai Strike, which has a chance to inflict Assist Break, and EX Iai Strike, which may cause EX Break on an opponent in EX Mode.
Dissidia Final Fantasy NT
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Dissidia Final Fantasy Opera Omnia
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Iainuki is the EX ability of Bartz. It becomes available to him upon equipping his EX Weapon Great Sword.
Pictlogica Final Fantasy
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Pictlogica Final Fantasy ≒
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Final Fantasy Airborne Brigade
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Final Fantasy All the Bravest
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Iainuki is the ability that is used by the Samurai during battle.
Final Fantasy Record Keeper
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Final Fantasy Explorers
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Final Fantasy Brave Exvius
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Iai Strike is a special ability that allows the user to inflict instant KO to all enemies. It has a 30% chance of succeeding and costs 12 MP to cast. It can be learned by Cyan (level 60, 4★) and Gilbert (level 75, 5★).
Gallery
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Etymology
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Iaijutsu (居合術, "Re-sheath Techniques") is a Japanese quick-draw style, often involving a drawing strike from the sheath akin to battoujutsu, but is distinctively characterized by re-holstering the sword into its sheath right afterwards. It may be used aggressively to wage a premeditated surprise attack against an unsuspecting enemy and is also a counterattack-oriented art.
In fiction, iai is often characterized with extreme speed, as if both the drawing of the blade and re-sheathing of it are done in an instant.