Sword Art Online wouldn’t live up to its name if the series didn’t have impressive sword abilities possessed by the most powerful characters. As Kirito defeats foe after foe and climbs the floors in Aincrad alone, he develops a sword skill entirely unique to him in the original VRMMORPG, Sword Art Online, called the Dual-Wield Sword Skill.
Unlike ALO or Underworld, Sword Art Online never implemented a magic spell system. (Though magic weapons and items do exist in the game.) Instead, players must practice weapon-based skills and maneuvers to level up and take on enemies. As a master of the sword and highly experienced fighter, Kirito eventually unlocks the rare Dual-Wield skill, making him unrivaled in combat.
Also translated as “Two Sword Style,” Dual-Wield grants Kirito the ability to equip two different blades simultaneously, but also grants him special new sword skills. However, a player doesn’t have to have Dual-Wield in order to fight with two swords at once -- the ability simply endows the user with unprecedented power. According to the Sword Art Online game's creator, Akihiko Kayaba, this special ability is only given to the player with the fastest reaction time of all.
Dual-Wield not only includes bonus stat bumps to attack speed, weapon defense, and cooldown time, but also signature techniques such as Cross Block (a defensive skill) and Double Circular (a two-hit combo) as well. Two epic techniques with staggering damage output are also unlocked: Starburst Stream (a 21-hit combo), and the Eclipse (a 27-hit combo). Kirito first demonstrated Starburst Stream on the 74th floor Boss “The Gleam Eyes,” which finishes the giant goat demon off. The Black Swordsman also showed off Eclipse when fighting with Kayaba in the finale, though his sword the Dark Repulser breaks from the clash against his opponent's shield.
Kirito first noticed he had access to the Dual-Wield skill in his stats in Season 1, Episode 8, after he defeated the bandit guild Titan's Hand. He didn’t know how the skill got there, but eagerly sought another sword to complement his signature blade the Elucidator. This spurred his adventure to gather the Crystalline Dragon Ingot for Lisbeth to create the Dark Repulser, also known as Sunlight Heart. To avoid drawing attention to himself, Kirito initially hid the skill until he found it absolutely necessary to draw both swords for combat.
While Kirito is certainly special for possessing his Dual-Wield feature, he’s not the only player who gained access to a Unique Skill. For example, Heathcliff, who is later revealed to be the antagonist Kayaba, has the Divine Blade skill which allows the player to switch between offense and defense at will. This ability is supposedly unlocked by the strongest player in SAO, but it’s not unlikely he simply gave it to himself considering he created the game.
Unique Skills stand as evolutions of the Meditation skill and only become available to those with a stat proficiency of 500 or above. Out of the 10,000 people trapped in Sword Art Online, only ten people had these Unique Skills. Other examples of these skills include “Infinite Spear” for the best two-handed lance user and “Darkness Blade” for the one who kills other players the most.
It’s never revealed to whom all of these skills became available, but if Kirito’s excellence with Dual-Wield proves anything, it’s that Unique Skills bestow game-breaking capabilities. No one in Sword Art Online seems to be able to match Kirito in speed – though Asuna the Lightning Flash by his side certainly comes close, even without an overpowered Unique Skill like Dual-Wield.
