Sailor Cosmos

Rumours and the Anime
Don't listen to the rumours that say Chibi Chibi is Usagi's 2nd daughter, or Chibi Usa/Rini's daughter. None of it is true. And if you only know who Chibi Chibi is according to the anime, you're in for a big shock. In the anime, Chibi Chibi is a little girl who is revealed to be the star seed of Sailor Galaxia (the main enemy in the last season of Sailor Moon called 'Sailor Stars'). Galaxia was a great soldier who battled 'Chaos' and contained Chaos in her body. But Chaos begam to take her body over, so Galaxia sent her star seed out into the universe to find someone that would nurture it. It found Usagi and turned into an adorable girl named Chibi Chibi. This is NOT what Naoko Tackuechi, the creator of Sailor Moon intended Chibi Chibi to be. Chibi Chibi's background is MUCH more complicated and even more beautiful.

The Manga: Ultimate Form of Sailor Moon
Originally, Chibi Chibi is the younger disguise form of a woman named Sailor Cosmos. Sailor Cosmos, though, is the ultimate, and final form of Sailor Moon. Confused? I'll explain.

Sailor Cosmos is one of Sailor Moon's Incarnations
Sailor Moon has many incarnations, she was Princess Selenity, then Usagi, then she becomes Super Sailor Moon and then Eternal Sailor Moon, then Neo-Queen Selenity, next, she becomes Cosmos. Her ultimate form is very different from the way we know her. The symbol on her forehead is different, but her hair, her features, all are pretty much the same. When she was Selenity she didn't look like Usagi does now - granted the manga draws the two to look exactly alike in order to keep the reader's understanding, and so it's less confusing as to who is who. In the future, as Cosmos, she will also look different.

What happened to Cosmos?
When Sailor Moon is Cosmos, she faces great death and destruction. All her loved ones are taken by Sailor Chaos. Facing all this, Cosmos decides to go back to her past, when she was Eternal Sailor Moon and help her past self defeat Chaos in the battle at the Galaxy Cauldron. But Cosmos doesn't go as her present form, she changes herself into a young girl, named Chibi Chibi.

Why Chibi Chibi?
The form of Chibi Chibi is a disguise. Sailor Cosmos can't go back looking like herself because she looks practically exactly like Usagi and especially since during the last 3 mangas all these new sailors are showing up and turning out to be enemies. Sailor Cosmos could be thought to be an enemy but a sweet innocent lil child like Chibi Chibi would be protected and yet be near everything to change the past.

Cosmos' Mission
Manga Vol. 18 - Eternal SM learns that the villain chaos has been absorbed into the Galaxy Cauldron - the place where all her fellow senshi, and all the stars and soldiers are born and return to. What Sailor Cosmos/Chibi Chibi wanted was for Usagi to destroy the cauldron because Chaos was in it. That way Chaos couldn't be reborn to wreak havoc and kill everyone in Cosmos' own time. But Usagi said that to destroy the place where stars live and are born....would mean the destruction of everything. So she chose to let chaos remain in the cauldron.

This is the mistake Sailor Cosmos of the future wanted to rectify. She regretted the mistake she made those years back when (as Usagi) she let Chaos still live in the cauldron in stead of destroying it. But when faced with her past self's reason again - she realized that what she had done back then as usagi was the right decision all along. And that she would battle in the future to win back her loved ones.

Are they really the same person? How?
Guardian Angel One said it best when she wrote:

Cosmos fought in the war HERE (HERE as in this time and place), meaning she had to have been either one of the Quartet, Chibimoon, Galaxia, or... Sailor Moon.

"The me of here, too, was all alone. Always suffering. So I was always by her side, to support her. I was going to make her choose the right path this time...."- Usagi was really the only one who Chibi-chibi was with (she pretended to be Usagi's little sister). Sailor Moon was the only one who really made a decision concerning the Cauldron that would influence the way the future would turn out.

"Now Eternal Sailor Moon, who saved the galaxy, is the true Sailor Cosmos." This shows the title of "Sailor Cosmos" isn't a position, like "Sailor Mercury" or "Tuxedo Mask" or a name like "Luna" or "Chibi-Usa". It's something inside a person- something some one earns. Cosmos said in her Eternal form, Sailor Moon was the true Cosmos, and in time, she would completely earn that gift once more. But she must remember that "matchless strength" of Eternal Sailor Moon and strive to be like it.

"Because I was blessed with great power by Eternal Sailor Moon. All the courage and strength to stand alone, the courage and strength to accept everything! I had forgotten it. The matchless strength!"

What about the sign on her forehead? That they're both in the same place at the same time?
There are 3 ways to answer this question:

1) Naoko made a mistake - when writing the ending - and forgot that she had stated before that both forms of Usagi couldn't be in the same time and place
2) Sailor Cosmos is an incarnation of Usagi not just a future form. their bodies are different just like Princess Selenity of the moon kingdom and Usagi of the present are not the same bodies
3) Cosmos seems to have a lot of power - she could have changed her form to Chibi-chibi, thereby becoming a "different person". After Sailor Moon sacrifices herself into the Cauldron, only then does Chibi-Chibi become Sailor Cosmos, her true form.

As for the difference between a CRESCENT MOON symbol and the STAR symbol on their heads, again 2 possible answers:

Neoqueen and Present Usagi were the same person from blood to skin cells, however Usagi is not physically the same as her ultimate form, Cosmos. Just like Princess Selenity is nothing like Usagi in present day.
When Minako first appeared, she had a crescent moon everytime she transformed, until Usagi was revealed to be the true Moon Princess, and then it faded away. If you can make a sign where there is none, you can probably change a sign. And Usagi seems to have the ability to make the sigil disappear- she could simply hide it then wear another one.

Lastly, the manga is ALL ABOUT Bishoujo Senshi Sailor Moon
The fact of the matter is that the manga is called Bishoujo Senshi Sailor Moon - the entire manga revolves around Usagi. It tracts her entire life history from her past forms to her future forms and gives us a glimpse into what her final destiny will be. Cosmos and Usagi look far too similar, the comments and the situation at the end of the manga, all the evidence is too much to deny.