Sailor Cosmos is best known as the true identity of Chibi Chibi, revealed near the end of the Sailor Moon manga's Stars arc. She's essentially Sailor Moon's ultimate future form—though Takeuchi deliberately left the exact nature of that relationship ambiguous, and has suggested the ambiguity was intentional even for herself.
Cosmos comes from a devastated future where she's spent ages fighting Sailor Chaos, only to watch everything she knows get destroyed anyway. Overwhelmed and hopeless, she does something drastic: she travels back in time as an infant version of herself to guide her past self toward victory. Her plan is straightforward—destroy the Galaxy Cauldron, destroy Chaos before it becomes a threat.
But Eternal Sailor Moon refuses. She realizes that destroying the Cauldron means no new stars will ever be born, and she won't trade the universe's future for safety. Instead, she sacrifices herself to it. That act of courage and selflessness changes everything for Cosmos. She realizes Eternal Sailor Moon embodies what true Sailor Cosmos actually is—not power or victory, but hope and strength. Inspired, Cosmos returns to her own future determined to fight again, this time with the resolve she was missing before.
What happens to her after that isn't spelled out. The manga leaves her fate open.
Cosmos never appears in the anime adaptation (though Chibi Chibi's adult form, the "Light of Hope," visually echoes her), which Takeuchi has said she regretted. In the manga, her brief appearances raised more questions than answers about her nature, but that uncertainty is sort of the point—she's meant to be mysterious, even ambiguous.
Content compiled by AnimeList.moe from publicly available sources.
