Quetzalocoatl (usually referred to as Lucoa) is a friend of Tohru.
Lucoa normally takes the form of a human woman with a voluptuous figure. She is the tallest among all female dragons in the human world. Her human appearance has long, wavy light green hair with more light green and blue shading that reaches her waist. Her scales form a black tank-top and mini-jean pants with black stockings, pink sneakers and a pink cap, with her outfit making frequent changes in the anime. She has a pair of brown horns coming from her cap.
In her dragon form, Lucoa is a black-feathered serpent with gold-colored markings on her face.
She is a calm, easy-going and laid back dragon, and has much better perception when it comes to what consists of normal human behavior (except, perhaps, for Elma). However, she easily gets flustered if her past is mentioned, which consisted of an incident with her sister that got her fired from being a Goddess. She also gets flustered if her plan backfires; shown in one of the episodes when she dresses Shouta in the Little Match Girl's outfit, only to have him run away in embarrassment.
In the past, Lucoa was worshipped by the Aztecs as a goddess until she unknowingly drank a cursed liquor given to her at a party, which caused her to sleep with her sister, something she is deeply embarrassed and ashamed about even centuries later. Incest was strictly forbidden in Aztec culture and it infuriated the other God's when they found out what happened, this act removed her of goddess status but was still in charge of creating civilization.
Quetzalcoatl came to the human world because of her curiosity about Tohru, who is living happily with Kobayashi. Some time later, while on a walk, she sensed someone holding a summoning ritual nearby. Curious about who might be holding such a ritual in the human world, she appears on the scene to answer the call, only to discover Shouta, a child from a family of mages, has been trying to summon a Demon. Lucoa decides to stay on as his familiar, although she struggles to gain his favor as he mistakenly thinks she's a Demon or Succubus due to her curvaceous body.
Lucoa is based off of the Aztec god Quetzalcoatl, who is normally depicted as being male.
- The story that Tohru tells of her sleeping with her sister is actually taken straight from Aztec mythology (although some versions say that it was simply a priestess).
Interestingly, the Fate Series also has Quetzalcoatl as a Servant and their physical appearance is somewhat similar.