According to tradition, Guaraci, the sun god once got tired of his eternal job and had to sleep. When he closed his eyes the world fell into darkness. To brighten the darkness while sleeping, Tupã created Jaci, the moon, to illuminate the night and bring softness and charm to the world.
Jaci was a goddess so beautiful that when Guaraci awakened by her light, he fell in love with her. And so, enchanted, he went back to sleep so he could see her again. But when the sun opened her eyes to admire the moon, everything lit up and she went to bed, fulfilling her mission. Guaraci then asked Tupã to create Rudá, the love and its messenger. Love knew no light or darkness. It could unite them at dawn. In this version, when an eclipse happens to be solar or lunar, it is the moment in which Jaci and Guaraci are together falling in love more and more.
Although some versions say that she is married with Guarací, the Sun God, the most famous one is that she is his twin sister and that she is the wife of the God of Thunder, Tupã. As the wife of Tupã, it is said that they were the first couple ever. In the some variations of her stories, she was even created by Guarací, because when he slept, the world was in darkness.
As Tupã created her, she is considered his daughter, but she is also considered his sister as there is a belief that Tupã said "I will not have only children, because all are my brothers, and sisters, even if they come from me". With the help of Jaci, Tupã descended to Earth in a place described as a mountain in the region of Areguá, Paraguay, and from this place created everything on the face of the Earth, including the ocean, forests, animals and the stars were placed in the sky at that time.
Jaci as a male
It is said that Jaci descended from the heavens as a male at times and brought virgin maidens to become stars at his side. But there was an Indian girl called Naiá who fell in love with Jaci. Naiá, always "chased" the moon, going to the place where Jaci went to fetch the virgins, but she always fell asleep, unable to see Jaci, and woke up just before dawn, when she saw the moon fading away. She ran through the forest chasing the moon but never reaching it. After some time, Naiá was languishing, becoming increasingly sick, because she refused to eat or drink until she found the moon. One day, she fell asleep in the spring of a lake, and woke up at dawn, seeing the reflection of the moon. Believing the moon was bathing in the lake, she jumped in the water but soon began to drown. Upon seeing that, Jaci decided that she would be a star, not in the heavens, but in the waters. Jaci turned her into an aquatic plant whose appearance resembles a star and to this day Naiá is there, but now she does not wait for her goddess. Naiá today is a beautiful "victoria regia" the star plant, the Jaci plant.
Influence in the water
Because of the lunar influence in the water, she is considered at some extension the goddess of the waters. Not only because of Naiá's story, but also because some versions say that she was responsible for the rebirth of Iara. For when Iara died and her body was thrown on the river, Jaci was responsible for bringing the fierce and beautiful indian warrior back to life as a mermaid and also as a goddess. Some versions also say that she is also Iara's sister.
Devoured by the Jaguar
A Tupinambá myth says that the moon is threatened to be eaten by the jaguar, the planet Mars, blood red.
"But we who are strong do not fear. So we continue to kill and eat enemies. As long as the jaguar does not eat the moon. " fragment from the myth of the Jaguar devouring the moon, non-official translation from portuguese.