Who Is Sailor Chibi Chibi?
Anime
In the anime she's Sailor Galaxia's starseed. SailorGalaxia had trapped Chaos in her body, but Chaos started taking over Galaxia's body, so Galaxia sends her starseed out of her body to find a warm light to nurture it, someone who will one day, use that starseed to destroy the Chaos inside her by destroying herself. The starseed became ChibiChibi. The light that ChibiChibi found was the light of SailorMoon. When the time arrived, ChibiChibi actually asks SailorMoon to follow Galaxia's wishes, but SailorMoon refuses to fight and kill Galaxia. Galaxia shatters her own star seed... and ChibiChibi dies. But SailorMoon finds the good still alive inside Galaxia, and Sailor Galaxia manages to defeat Chaos inside her! And when Chaos was defeated, the starseeds that were collected are restored, and the Sailor Senshi, who had died during the battle, come back to life, and so does ChibiChibi who now has to leave, because her mission was accomplished and the Galaxy is safe.
Manga
In the manga, she is Sailor Moon's ultimate form, Sailor Cosmos, the most powerful senshi in the Universe, and the final form of SailorMoon herself! She had traveled to the present to convince EternalSailorMoon (herself) to destroy the Cauldron, thus eliminating Chaos. *The Cauldron is the source of all stars and Chaos merged herself with it and took over.*
In the future, Cosmos knew nothing but devastation and death. She thought that traveling back to the past and destroying the Cauldron would end the future suffering. But she learns courage from SailorMoon, and also hope, that the future can be a beautiful place even with Chaos in it. She realizes that destroying light and life along with darkness and death is no solution at all. After sending the Asteroid Senshi on their way to the future, she leaves.
.:
Back:.