Chaos

カオス

In the manga, Chaos is an entity trapped within the Galaxy Cauldron that failed to become a star. It dispatches incarnations as Sailor Moon's primary adversaries—Queen Metaria, Death Phantom, Pharaoh 90, and Queen Nehellenia—and ultimately employs Sailor Galaxia to steal Sailor Crystals, aiming to liberate itself and dominate the galaxy. Visually, it appears as a vast mass of black fourth-dimensional space. Ultimately, Sailor Moon forces it back into the Galaxy Cauldron, causing everyone killed to return to their home planets and eras, reincarnated after the conflict. However, indications suggest Chaos is not dead and will return as Sailor Chaos, mirroring its role in Sailor Cosmos's future.
Sailor Chaos represents Chaos reborn. According to Sailor Cosmos, Chaos will emerge from the Galaxy Cauldron, reborn as a powerful Sailor Senshi. Frustrated by an ongoing battle against Sailor Chaos, Sailor Cosmos disguised herself as Chibichibi to travel back in time and persuade Sailor Moon to destroy the Galaxy Cauldron, thereby preventing Sailor Chaos from emerging and initiating a new series of devastating wars.
Sailor Chaos never appears in the anime, though Chaos makes a brief appearance in episode 200, expelled from Sailor Galaxia after her defeat. Beyond this, Chaos does not appear in the anime series. Sailor Galaxia ultimately reveals herself as the soldier who sealed Chaos within her own body, thus saving the galaxy. Chaos possesses Galaxia to grant her the power to fight the kibou no hikari—the Light of Hope—Eternal Sailor Moon. However, Usagi manages to reach the small fragment of hope remaining in Galaxia's heart, leading her to release Chaos from her body and conclude the anime story arc.