Mickey... You're too late.
Anti-Aqua is a boss in Kingdom Hearts III. She is under Master Xehanort's influence due to her corruption at the hands of Ansem. Sora is forced to fight her in order to release her from the dark corruption.
Unlike Aqua, which is usually altruistic, Anti-Aqua is bitter, angry and cruel. She is particularly resentful of King Mickey, whom she accuses of having abandoned her in the Dark World for more than a ten years, claiming that her loneliness and fears have made her feel despair and misery.
Anti-Aqua is a corrupted version of Aqua. Her hair is bleached blue, her eyes are yellow, and her once-white dress has darkened and become tattered. Her arms and legs have also begun to darken, and her hands are now black with red fingertips. In battle, she wields Mickey's Star Cluster.
When she first reveals herself, Anti-Aqua initially appears as a black silhouette wreathed in a violet aura of darkness.
Ansem, Seeker of Darkness arrives at the Dark Margin to confront Ansem the Wise about the children the former king used in his research. Aqua tries to fight Xehanort's Heartless, but the Heartless subdues her, imbues her with darkness, and throws her into the seas of the Dark Margin.
The corrupted Aqua, now known as Anti-Aqua, later confronts King Mickey and Riku when they return to the Dark Margin to find her. She has a Demon Tower restrain Mickey before revealing herself and explaining the pain she has been through over the years she spent trapped in the Realm of Darkness. She and the Demon Tide then team up to fight Riku, but with Sora's help, Riku is able to defeat the Demon Tide and free Mickey. With Mickey and Riku out of commission, Sora then battles Anti-Aqua and successfully manages to free her from the darkness.
Anti-Aqua behaves nearly identically to Phantom Aqua from Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-. She begins the fight by activating Spellweaver and continues to fight in this mode. From there, she attacks by firing homing orbs at Sora and performing spiralling attacks with doppelgängers. All of these attacks can be blockable. She can occasionally teleport across the arena, and sometimes teleport before Sora can attack. When her retaliation point is reached, she often counters with an unblockable lunge.
As her health dwindles, Anti-Aqua gains access to two ultimate attacks. The first, in which she teleports in the air before firing Blizzard shards, can be guarded or evaded. The second is the Spellweaver finisher, where she and three clones perform a spinning attack. Sora must dodge out of the spiral before the Anti-Aquas finish the attack.