The "Galaxy Cauldron" is the most powerful star in the universe responsible for the cycle of life and death of all things. It is located at the center of the Milky Way galaxy, at the core of Sagittarius Zero Star.
Everything is created and destroyed within the Galaxy Cauldron - it is the source of all star seeds. All stars and planets start as tiny star seeds within the Cauldron. Star seeds form the core of all life on these heavenly bodies as well with special star seeds growing alongside them to eventually become their Sailor Guardians. The star seeds which depart from the Cauldron can travel not only through space to their destinations but also through time. When their lives are over, the fragments of these dead stars return to the Galaxy Cauldron and can be witnessed as an endless procession of butterflies.
The Galaxy Cauldron is a sea of possibilities. Every star seed which has, can, and will exist is melted down and indistinguishable within it. As such. everything was once together within the Cauldron. Furthermore, if the future is changed so that a certain star seed will not be born they will continue to exist within the Cauldron as it is the source of infinite possibilities. Those who return to the Cauldron can also be reborn later as they continue to exist within it. It creates both light and darkness making not just Sailor Guardians but is also responsible for Chaos and her incarnations of darkness. It is very difficult for one to retain their form within it though a few have done so including Guardian Cosmos, Queen Serenity, Usagi, and her Sailor Guardians.
The Cauldron first appears in Usagi's dream where, manipulated by Chaos, Sailor Galaxia intends to lure Usagi to the Cauldron. Sailor Moon proceeds to fight her way through the defences of Sagittarius Zero Star to reach Galaxia. Soon after Sailor Moon reaches the Cauldron, Sailor Galaxia throws most of the galaxy's Sailor Crystals into the Cauldron and Chaos reveals herself to be fused with the Cauldron itself. Chaos intends to usurp the Galaxy Cauldron as the most powerful star and to rule the universe in its stead.
Chibi Chibi tells Usagi the only way to permanently defeat Chaos is to destroy the Cauldron as well. This leaves Usagi with a choice: destroy Chaos, along with the Cauldron, thus ending all war but eventually the future itself, or preserving the Cauldron and hence all future stars but allowing Chaos to return someday. Chibi Chibi tries to convince Sailor Moon that destroying it to end all suffering is the right thing to do, but instead Sailor Moon tells Chibi Chibi to not give up on her future, to always have hope, and that living life was more important even if it comes with suffering. Sailor Moon then threw herself into the Cauldron dragging Chaos down with her, dissolving the dark entity. While doing so, Sailor Moon uses the Lambda Power of the Cosmos Crystal to regenerate the Galaxy Cauldron and the galaxy to their original forms.
Guardian Cosmos, the small but powerful guardian of the Cosmos Crystal, who resides within the Galaxy Cauldron. When she saw Usagi in the Cauldron, she was surprised that Usagi and her friends could retain their physical forms within the Cauldron. She asked Usagi if she had come to the Cauldron to throw her life into it and start a new star's history, or if she wanted to live as she was. Given the choice, Usagi said that she wanted to live her life as she was, no matter how difficult it might be, to build a future together. Guardian Cosmos granted their wish, and as they were being pulled away, Usagi asked about Chaos. Guardian Cosmos told them that Guardian Chaos and the Chaos Seed had been dissolved into the Cauldron, but could be born again.
- In various mythologies, Butterflies are a common symbol for the soul and the cycle of life and death. Those returning to the Cauldron take this form.
- Act 59 - Galaxia: "This Cauldron - THIS is the most powerful star in the universe! It is absolutely invincible!"
- Act 60 - Sailor Cosmos: "This is the Galaxy Cauldron. Where all the galaxy's stars are born and where they return at their journey's end."
- Act 59 - Galaxia: "The holy land of the stars, The Galaxy Cauldron. Strong stars and weak stars. Trash and Sailor Guardians. This is the place where all the stars throughout the galaxy are born."
- Act 59 - Sailor Moon: "We want to be united. Together as one. Because that's how we were in the beginning."
- Act 60 - Sailor Cosmos: "Through Eternal Sailor Moon's power, the Cauldron, and the galaxy, were able to reclaim their original forms..."