Magical beings that come from a separate universe. People are able to form contracts with them to use.
Celestial Spirits are magical beings that reside in a another dimension. They all obey the Celestial Spirit King who governs their world and laws. Humans are able to summon them by receiving their Gate Key or by finding one. The Spirits then form contracts with their owners so that they are able to know what days to use them. The celestial Spirits also has rules the Mages most follow. One is that humans are not allowed into their world. If this happens the mage losses their contract with said spirit. The rule also applies to their mage being arrested or dead. The Spirits must also follow a rule. The spirits must are not allowed to kill their contractors. So far their are two types of Gate Keys. The gold keys belong to the Ecliptic Zodiac who have one of 12 keys for each Spirit while there are many of the Silver Keys.
Aquarius - A celestial spirit in the form of a Mermaid. She has control over water and is the girlfriend of Scorpio. She is currently owned by Lucy Heartphilia.
Aries - A timid female spirits with small horns on her head and wears white fluffy clothes. She was originall owned by Karen Lilica but now belongs to Angel.
Cancer - A tall attractive man with crab legs on his back who carries a pair of scissors. He mostly uses the scissors for cutting hair but sometimes uses them for combat. He is currently owned by Lucy Heartphilia.
Capricorn (aka Caprico) - A tall Goat Man that's key originally belonged to Layla Heartphilia. He became possessed by a mage named Zoldeo for 17 years and became a member of Grimoire Hearts, Seven Kin of Purgatory. Once freed he gladly gave his key to Lucy due to the promise he made to her mother.
Gemini - Two spirits named Gimi and Mini that can transform into anyone perfectly and replicate both their thoughts and magic abilites. They originall belonged to Angel but decided to join Lucy Heartphilia because of her kindness towards the other spirits.
Leo (aka Loke) - A attractive man who is skilled in unarmed combat. He orginally belonged to Karen Lilica but became angry with her for how she treated Aries. So he forced himself to stay in the human world until she severs his and Aries contracts with her. However when he returned to the village she lived he discovered she was killed (by the Oracion Seis guild member Angel). Thus her being dead Loke though he broke the celestial spirit rule towards humans. So he joined the Fairy Tail guild. Soon Lucy discovered who he really was and helped him return to their world. He also gave her his key for thanks in helping him.
Sagittarius - A man who wears a horse costume and wields a bow and arrow. He currently belongs to Lucy Heartphilia.
Scorpio - A man who wears a trench coat and has a metal scorpion tail which is a gun. He is also the boyfriend to the celestial spirit Aquarius. He is currently owned by Angel.
Taurus - A Anthropomorphic bull who carries a large axe and is very strong. He is currently owned by Lucy Heartphilia. He also has a crush on her.
Virgo - A maid who wears shackles around her wrists. She has the ability to tunnel underground. She is also very loyal to her master and does whatever they command. She even can change her appearance to her master liking. She originally belong to Duke Everlue who demanded her to be fat and muscular. She also demands to be punished after her task is punished by her master. She now belongs to Lucy Heartphilia after Duke Everlue is arrested.
Caelum - Caelum is really a weapon more than a being. It can change into a sword or a cannon.
Crux - is a human like cross with a mustache and cross shaped nose. Lucy Heartphilia owns a Crux key.
Horologium - A clock with a face and pair of arms. His doesn't have many abilites but is mostly used for defense by it's owner who can stay inside his body for protection. Lucy Heartphilia owns a Horologum key.
Lyra - A little girl who has wings and wears a bonnet and a dress. She also carries a harp for which she uses to sing or perform songs for her master. Lucy Heartphilia owns a Lyra key.
Nikora - "The Canis Minor" Nikora (or Plue, which Lucy named hers) is a cute, yet small creature which resembles Plue from Rave Master. Nikora hardly takes up magic power when summoned and is mostly used as a pet.