Act 51 Stars 9
Sailor Cosmos is a Sailor Senshi who appears in the last two acts of the manga. She comes from a distant future, where all was destroyed because of the battle with Chaos. After a long time fighting, she fled to the past in the form of Chibi Chibi to encourage Eternal Sailor Moon to defeat Chaos in the final battle of the series. Sailor Cosmos is thought to be the future Sailor Moon.
Sailor Cosmos does not appear at all in the anime, though many fans have mistaken a screenshot silhouette for Sailor Cosmos.
However, they cannot be the same character as Chibi Chibi is Sailor Galaxia's star seed. This screenshot happens during episode of the original anime. Episode 200. As a star seed in the anime only, Chibi Chibi has many forms. She looks like a typical golden star seed when Galaxia casts her out of her body to protect her from Chaos's influence. Galaxia pleads with her starseed, which she has dubbed The Light of Hope, and tells her to find a new host, someone more worthy of carrying her star so that it will escape Chaos's influence. It then changes into a red sparkly butterfly and travels to Earth, having selected Usagi to be her new host, thus the reason for her new form of an adorable little girl who looks like a mixture of Chibiusa and Usagi with pink hair and blue eyes and heartshaped odango's with a similar personality and appetite.
We also see later on that she takes the form of a senshi, Sailor Chibichibi(No planet or moon name, simply Chibichibi as her character until her identity is truly revealed is meant to be ambiguous). During the final battle she also forms into a sword and back into her star seed where a silhouette is then seen walking to the floating and injured Usagi, the light hiding all of the silhouettes features aside from having hair like Eternal Sailor Moon, a skirtm wings and a cape. We can assume that if Usagi had fully grasped Chibichibi as her own star seed, that the form we see for a brief moment could have been Usagi's new form since Chibichibi's little girl form was based on how Usagi looks in order to get close to her since she is the one worthy of being the new host. However that is in theory and nothing has ever been stated about the shadowy figure, not even her name.
Sailor Cosmos only appears in the last arc of the manga.
Sailor Cosmos comes from a far distant future where Chaos has been reborn as Sailor Chaos. There is not much stated about the battles only that Cosmos had fled because already too much had been lost and for her, to continue fighting was no longer worth it as she lost everyone and everything to the battles.
She flees through time and disguises herself as Chibichibi in order to get close to her past self.
A lot of fans seem to be confused on whether or not Sailor Cosmos really is Sailor Moon/Usagi Tsukino's future self. Naoko Takeuchi had been stated in an interview that Sailor Cosmos is Sailor Moon's future form in 1998 during the San Diego Comic Con and for Smile Magazine(No longer in circulation).
A lot of people have tried to claim that there is a different Sailor Moon in the future, or that perhaps she is a descendant or reincarnation. However the manga clearly states that when Cosmos had disguised herself as Chibchibi she did so in order to "Get closer to her past self" which was Usagi Tsukino in her human form rather than her Sailor Moon form where a picture shows ChibiChibi cradled in Usagi's arms. If it were a different Sailor Moon, she would have gone to a different time and person and there would have been no need for the flashback sequence showing Usagi while Cosmos said this.
The descendant theory is also off the table because if she were, then when Chibiusa disappeared, so would have Cosmos if they were related and she did not disappear. It is also stated several times over that the Queen only has one child, and if Chibiusa disappeared, all following generations would have disappeared along with her.
As for being a reincarnation it is entirely possible. We are not given much about the time where Cosmos comes from only that it is in a future far past Crystal Tokyo and she is indeed a future version of Sailor Moon/Usagi Tsukino. The consensus among fans is that Cosmos fled the fight because she was losing or she had been defeated but no where in the manga does it say that. This rumor was started when fans compared her fleeing and trying to get to her past self, Eternal Sailor Moon to destroy the Galaxy Cordon in order to destroy Chaos so he will never have a chance to be reborn as Sailor Chaos. However, this is not true. Cosmos came to the conclusion to go back in time to defeat Sailor Chaos by remembering the battle she had originally had with him when she was Eternal Sailor Moon and he was only a shadow entity and not a senshi. Everything in her world was lost and gone, and she felt that the future she had come from had become so horrible and terrible and was filled with nothing but pain and loss that it would be better to destroy the entire galaxy then let Chaos have the chance to be born as Sailor Chaos. The loss outweighed staying and winning in her mind
So the truth would be that she did not run away because she was losing the battle but that she had lost everyone and everything that had ever been important to her, and as we know from her time as Sailor Moon, her loved ones and the people of Earth, were the reason she kept fighting to begin with. It's understandable that after losing everything and everyone she would act this way. In pleading with Eternal Sailor Moon to destroy the cauldron, she is reminded of how she became Cosmos to begin with as she witnesses Eternal Sailor Moon's courage and self-sacrifice for the ones she loves. Cosmos tells Eternal Sailor Moon she becomes Cosmos when she is gifted with the Lambda power(the ultimate power, the power of hope) when she loses everything and everyone, so that she can save everything and everyone.
Reminded of her true power, she goes back to her future to defeat Sailor Chaos because she knows that despite losing everyone and everything, she can still see be with them again through the power of hope.
- Sailor Cosmos is the last Sailor Senshi to appear