Aquarius is a Celestial Spirit with the appearance of a royal blue Siren. She has a Aquarius zodiac symbol tattoo on her collar bone.
Aquarius is a very moody and ill-tempered Celestial Spirit who often threatens to kill her Lucy. Unlike other Celestial spirit who serves and obeys Lucy, Aquarius is irritated by Lucy. When she is summoned, she will either attack the opponent or Lucy or both depending on her mood. She is sweet, loving and caring to her Boyfriend Scorpio to which she shows her other different side.
Her previous owner was Lucy Heartfilia's mother, Layla Hearfilia who Aquarius deeply cared for. When Layla retired, Aquarius' key was entrusted to another mage who was instructed to give her key to Lucy if Lucy decides to become a mage. Aquarius' is Lucy's first celestial spirit and key.