Aqua

Aqua is one of the main protagonists of Kingdom Hearts Birth by Sleep. From the view of the story, it is revealed she is one of the Keyblade Wielders before Sora. Like Terra and Ventus, it is her dream to become a Keyblade master, a dream she is the only of the three to accomplish.

While her name means "Water" in Latin, Kairi's name in Japanese means "Sea". The only connection between the two is that Aqua met Kairi in Radiant Garden in Kingdom Hearts Birth by Sleep and put a protective spell on her necklace, which later brought Kairi to Destiny Islands. Kairi, by accidentally touching Aqua's Keyblade during this time, also inherited the Keyblade from Aqua.

Kingdom Hearts Birth by Sleep
After Terra and Ventus, Aqua was the last apprentice to be sent by Master Eraqus to seek out Master Xehanort and his cohort Vanitas who had previously disappeared. Aqua is known to be a level-minded person, but often worries about her friends. She takes the Master Qualification Exam along with Terra, and becomes a Keyblade Master. Aqua, Ven, and Terra come across many Disney characters along the way and fight of hordes of Unversed. Aqua later ends up at Radiant Garden with Mickey Mouse and meets the Princess of Heart, Kairi, who touched Aqua's Keyblade in fright, unintentionally performing a Keyblade Inheritance Ceremony. They protect her from a group of Unversed and in return Kairi gives Aqua flowers, which becomes the Keyblade, Destiny Place. She also places a protective charm on Kairi to help her in the future. At one point Aqua and Terra come to Destiny Islands and meet two young boys by the name of Sora and Riku. Aqua sees the strong bond between the two friends and advises Sora to help Riku if he ever falls into darkness. Aqua later encounters an unconscious Mickey drifting in space and takes him to the Mysterious Tower, where she hears of Eraqus's death from Yen Sid and heads to the Keyblade Graveyard to meet up with Terra and Ven. They are confronted by Master Xehanort and his apprentice, Vanitas and a great battle takes place. After fighting Braig and then Ventus under Vanitas' influence, Aqua loses consciousness and she ends up at Yen Sid's Tower with Ventus, who has lost his heart. After creating Castle Oblivion to keep Ventus's sleeping body safe, Aqua tracks down a possessed Terra to Radiant Garden.

Failing to bring Terra back to his senses, Aqua fights and defeats Xehanort, who would have fallen into darkness if Aqua hadn't saved him by sending her armor and Keyblade with him out of the darkness. Now stuck in the Realm of Darkness, Aqua is attacked by several giant Heartless, but is saved by Terra and Ven's Keyblades. With renewed trust in her friends, Aqua continues on.

Kingdom Hearts II and Kingdom Hearts II Final Mix
Aqua's armor and Keyblade were briefly seen in Kingdom Hearts II Final Mix. They reside in the Chamber of Repose, a room constructed by the Apprentices under Radiant Garden for an as of yet unknown purpose. Xemnas visits the armor often, calling it "friend" and talking to it for long periods of time. This has piqued the curiosity and suspicion of Xigbar, who often eavesdrops on his conversations, and once shared this story with Zexion, stating that one time he heard "another voice" respond to Xemnas. In The World That Never Was, Sora encounters Xigbar, who mentions "other Keyblade bearers", referring to Terra, Aqua, and Ventus.

Reconnect. Kingdom Hearts
Aqua ends up at the Dark Median, where she meets Ansem the Wise, who was cast into the Realm when his machine exploded. He reveals that in the Realm of Light, it has been almost eleven years, and he explains the events that have occurred in Aqua's absence, including the actions of Sora. Knowing that Sora will rescue her and her friends, she utters Sora's name with renewed hope.

Abilities
Aqua is described by Tetsuya Nomura as being "tricky". A magic-based fighter with agility to boot, she's capable of doing cartwheels while attacking with her Keyblade. While she's more than capable physically, her prowess lies with a more magic-oriented fighting style, being versed in all forms of it. Aqua is second only to Master Xehanort in terms of magic amongst Keyblade Users, displaying superior skill to both Terra and Ven as well as later Keyblade users such as Sora and Riku. She has her own special variations of the Fire, Ice, and Thunder spells, and can cast the Reflect spell indefinitely without tiring, effectively giving Aqua a 360 degree defensive zone. She can also augment her jumping abilities with magic. She is the slowest of the trio, however her slender frame makes her a difficult target. Small petals also appear when she summons her Keyblade. Her known Command Styles are:

Level 1 Command Styles

 * Magic Wish: Her own exclusive Command Style; it utilizes the power of light to hover her Keyblade in midair, swiftly attacking enemies while enhancing her magic capabilities as well. Activated by filling the Command Gauge with a variety of multiple magic-based commands.
 * Thunder Bolt: A swift Command Style that unleashes powerful lightning upon attacks. Activated by filling the Command Gauge with Thunder-based commands.
 * Fire Blazer: A ranged and versatile Command Style that focuses the Keyblade to erupt in flames while attacking. Activated by filling the Command Gauge with Fire-based commands.
 * Diamond Dust: An ice-based Command Style that seems to specialize in crowd-control and dealing with multiple enemies. Activated by filling the Command Gauge with Ice-based commands.
 * Ice Blast: Another ice-based Command Style that uses an ice cream theme. Randomly activated by filling the Command Gauge with an Ice Cream item.

Level 2 Command Styles

 * Ghost Drive: Aqua's high speed Command Style and exclusive to only her; it allows her to attack enemies at high speeds while using after-image illusions and tricky movements to her advantage. Activated by filling the Style Gauge with Thunder and Magnet-based commands.
 * Blade Charge: In this Command Style, the Keyblade resembles a Light-blue sword. A long-ranged style, as its name implies, it allows the user to "charge up" the attacks for additional damage. Activated by filling the Style Gauge with Fire and Ice-based commands.
 * Air Rider: A Command Style that gives Aqua a great midair advantage, it allows her to ride her keyblade around to attack foes from above at high speed. Activated by filling the Style Gauge with evasive, or Zero Gravity-based commands.

Additional abilities include:
 * Dimension Link: An ability that allows Aqua to summon character's powers from other worlds to aid her in battles.
 * Shoot Lock:
 * Rainbow Shower: Light in seven colors bursts from the Keyblade and chases after enemies. Press at the right time in the circle to input the command. “An attack with light in seven colors.” “A spiraling light whirlwind, a rainbow attack, again!” This move bears a slight similarity to Sora's Ragnarok technique.
 * Bubble Blast: A giant bubble appears around Aqua and attacks by releasing smaller bubbles that chase after enemies.
 * Shiny Bloom: Aqua twirls on the spot while shooting many orbs of white light. As it progresses, her spinning becomes more and more elaborate until she is spinning with one of her legs behind her head.

Personality
Aqua shows some similarities to Kairi, which she shows by making good luck charms for her friends. She also has a devotion to her friends similar to that of Sora's, for she did everything in her power to protect Ventus from harm and even sacrificed herself to save Terra. Her personality is serious, kind, strong willed, and responsible, as she is the most reliable of the three. She is always worrying about Terra and Ventus, who she treats as brothers. She has been shown to be blushing and embarrassed when Zack asks her to a date, shaking her head and arms in an attempt to compose herself. She seems rather modest, as despite becoming a master she still referred to herself as a trainee. The only time she referred to herself as "Master Aqua" was toward the end, when she fights the possessed Terra.

Appearance
Aqua looks slightly like Kairi, but older. She has blue eyes like the latter, but her hair is blue and shorter. She wears a black and blue, high-collared halter top, two pink, intersecting belts over her chest, and black shorts. She wears an odd silver badge similar to badges also worn by Ven and Terra, though Terra's is gold. On Aqua's arms are white bell-sleeves and tan, fingerless gloves. She also wears a small, segmented piece of armor on each of her upper arms. She wears what appear to be black stockings or socks on her legs which reach to about halfway up her thighs, leaving a small area of bare skin on her upper thighs. Aqua also bears two strips of blue cloth that drape over either side of her hips, along with a smaller, white strip of cloth tied around her waist, draped in the same manner. Finally, she wears pointed, armored, silver boots with a sharp "hook" on the outer side of each.

By touching the piece of armor hanging on her arm, Aqua will become full clad in her armor. In the Birth by sleep secret video, Aqua's armor is mostly colored in shades of silver, black, grey and blue. Notable additions include a silver breastplate resembling an upside-down crescent moon and a dark-visored helmet. Her helmet, like Ven and Terra's, bears two prongs on either side, with her silver ones wrapping around the sides and angling diagonally downwards. Her cape is that of a dusty-rose color. In Kingdom Hearts Birth by Sleep, Aqua's armor remains largely unchanged, though she loses her cape and grey becomes a more dominant color than black or blue. She also gains more armor near her upper legs and hips.

During the development for Kingdom Hearts Birth by Sleep, Aqua's outfit was altered, as Tetsuya Nomura considered her exposed back to be too revealing. As well, her eyes and hair were originally darker.

Trivia

 * The Japanese Kingdom Hearts Birth by Sleep website's startup screen refers to Aqua as the "Dancing Waters Forming Bonds" (絆繋ぐ舞水).
 * In Aqua's "Magic Wish" Mode, she can control her Keyblade using telekinesis, similar to Sora's Master Form and Final Form. She also shoots "Magic Bullets" similar to Sora's Wisdom Form.
 * Aqua is voiced by Megumi Toyoguchi, who previously voiced Paine in Final Fantasy X-2 and Kingdom Hearts II.
 * Aqua is one of only five characters in the series to call King Mickey by his name. Others include Yen Sid, Ventus, Riku, and Data Sora.
 * Aqua is the only one of three Keyblade wielders to have encountered all three of Sora, Riku, and Kairi. Terra has only encountered Riku, while Ventus has only encountered Sora using his lost heart.
 * Aqua fights both Terra and Ventus over the course of Kingdom Hearts Birth by Sleep. Twice with Terra during the Master Qualification Exam and during the Last Episode, and once with Ventus in the Keyblade Graveyard.
 * In the promotional art for the game, Aqua's back is almost completely cut off from view by the guard part of Terra's Keyblade. This could be because of the complications regarding Aqua's back design during the earlier development stages of the game, or because her appearance was in development at the time.