Aquarius

Aquarius "the Water Bearer" is a Celestial Spirit that is one of the 12 Golden Zodiac Keys. Her key is currently owned by Lucy Heartfilia.

Appearance
Aquarius is based off of a mermaid. Her tail, bikini top, and hair is blue. She has two gold armlets and she wears a jewel circlet. She wields an urn which is the basis of her powers.

Personality
Aquarius is very moody toward her owner Lucy (whether it's just to her or everyone is unknown). However she is very reliable in battle, although she tends to target Lucy as well as the enemy. She usually threatens that she'll kill her but she has yet to do so.

In contrast, she is very kind and lovable towards her boyfriend Scorpio to which she shows a completely different side of herself. She also goes as far as to threaten Lucy to keep quiet about her moodiness in front of Scorpio unless she wanted to be a "drowned corpse".

Magic and Abilities
Much like her name suggests, her magic deals with water. She absorbs water in her urn and she hurls them with tremendous force. She can cause a yacht from a few hundred miles out at sea back to shore. So far, Aquarius cannot be summoned unless there is a body of water (ocean, river, or a liquefied human.)

Macao arc
As Lucy and Natsu Dragneel fight Bora, Lucy summons Aquarius to send Bora's ship full of captured girls to the harbor. Happy does show a friendly interest in her given that she was a fish, to which she doesn't respond to. After doing her job, she states her desire to not be bothered for a week as her boyfriend is taking her on a vacation. Before she leaves, she rubs it into Lucy's face that she has a boyfriend while Lucy doesn't.

Galuna Island arc
Aquarius is re-summoned when Lucy battles Sherry to deal with Sherry's controlling abilities. Aquarius attacks Sherry along with Lucy because she didn't like being controlled. Before leaving Aquarius berates Lucy's personality claiming that is the reason she'll never get a boyfriend like her.

Tower of Paradise arc
Aquarius is summoned again when Juvia Loxar is controled by Vidaldus Taka. Juvia liquifies herself and Lucy takes advantage of the situation to summon Aquarius through Juvia. Aquarius attacks everyone and Juvia and Lucy Joins hands to use Unison Raid. After defeating Taka, Aquarius mouths off at Lucy, saying that she shouldn't ever summon her in such a strange place or she'll kill her, even wondering if she'll summon her next in a toilet bowl. She leaves again saying not to summon her for two weeks and commenting that Lucy should get a boyfriend.

Oración Seis arc
Lucy summons Aquarius as her strongest Celestial Spirit in her battle against Angel, especially since the battle is taking place at a river. Desperate to defeat Angel, Lucy tells Aquarius that she's free to do anything, including attack Lucy, so long as Angel is defeated. Aquarius agrees, but is removed from the battle when Angel summons Scorpio, who is revealed to be Aquarius's boyfriend, something that Angel was aware of but Lucy was not. The Celestial Spirits go off on a date with consent from Angel, much to Lucy's dismay. Lucy, forced to fight Angel without her strongest spirit, turns to summoning her trump card, Loke.

Edoras Arc
After Hughes dumps both Natsu and Lucy into a pond after a hellish roller coaster ride, Lucy then summons Aquarius to fight Hughes. However, Aquarius exclaims in shock, as she cannot control the water, because Hughes is controlling it.

Trivia

 * Her upper-body appearance is the same than Undine, the queen of water people, in Fairy Tale, a one-shot made by Mashima Hiro before Fairy Tail.
 * She can only be summoned on Wednesday.
 * In chapter 182, when Lucy summons Aquarius to fight Hughes, is the only time Aquarius has not argued with Lucy. It is suggested that Aquarius' attitude toward Lucy has been tempered by Lucy's ownership of Scorpio.
 * While Aquarius is associated with water (as the Water Bearer), the astrological sign of Aquarius is actually an air sign, not a water sign.