The Galaxy Cauldron was the birthplace of all stars and all living things in the galaxy. It was first mentioned in Act 55 of the manga, and was stated to be at the center of the Milky Way galaxy, in Sagittarius Zero Star. In the final manga arc, the Cauldron was taken over by Chaos, the purest form of evil, and Sailor Moon was faced with a choice: destroy Chaos and the Cauldron, thus ending all war but also all life, or preserving both, ensuring that life would go on but that war would as well. Chibi Chibi tried to convince Sailor Moon that destroying it to end all suffering was the right thing to do, but Sailor Moon told Chibi Chibi not to give up, to always have hope, and that living life was more important. Sailor Moon then threw herself into the Cauldron.
Guardian Cosmos, the small but powerful guardian of the Cosmos Crystal, resided 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, in order 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 would be born again.