Now that you have learned the truth of who Cosmos and Chibi Chibi are, here is the proof from Manga Volumes 17 and 18. Sailor Moon (c) Naoko Tackuechi. Summaries based on Alex Glover's translations. Background info: in the last volumes of the manga (and the anime series) Galaxia killed Mamoru/Darien and the other sailor soldiers by taking their sailor crystals. Galaxia then seeks to mess with Usagi/Sailor Moon's mind by taking Mamoru/Darien's sailor crystal (the Golden Crystal) and making him reappear - but it is not him - not his soul, just his appearance. Galaxia then, to torture Usagi/Sailor Moon, pushes Mamoru/Darien into the Galaxy Cauldron, to make Usagi think her Mamoru is dying again, a second time. Now here is where the summaries/translations begin.
Sailor Moon is fighting Galaxia, who has just thrown Mamoru/Tuxedo Kamen into the Galaxy Cauldron. Usagi screams and watches Chibi Usa (Rini - her daughter) fade out of existence. Galaxia tries to strike Sailor Moon, but Chibi Chibi appears and blocks her. Then a blast shoots forth from the Galaxy Cauldron, knocking Galaxia off the cliff. Sailor Moon grabs onto Galaxia, saving her and holds onto Chibi Chibi as well. Galaxia wakes up and asks Sailor Moon why she doesn't finish her off. SM says :
"I can't fight anymore," says Usagi. "Everyone is gone. All this time, it wasn't for peace and justice. I only fought for the ones I love, and my friends. But now they're all gone. If I don't have my most precious ones... For who, for what should I fight?"
Galaxia says if they fight together then maybe there will be an end to war. But then CHibi Chibi speaks up and this is what she has to say:
"No," says Chibi-Chibi. "The wars will not end. They will always continue. But you can end this war, the one now. To save the galaxy's future. Sailor Moon, with your last power, eliminate the source of all the enemies, Chaos and the Cauldron, and end the war! Chaos is now completely one with the Cauldron. To completely eliminate Chaos, there is no choice but to destroy the Cauldron."
"But if the Cauldron is gone, no more stars can be born! Someday the galaxy's future will be no more!" says Usagi
"But if you don't do that," Chibi-Chibi says, "this war and the history of suffering will continue forever! It will all be on your shoulders, Sailor Moon. You will regret this, Sailor Moon!" (she speaks with certainty and knowledge of this as a fact)
"Chibi-Chibi...?" Usagi looks at her. "As long as stars can continue to be born, war will not end," Usagi says. "The darkness calls to the light, and the light calls again to the darkness. Is this the will of the galaxy? Saying I will end the war...Will that be the end of everything? And that glaive of death, this time must I be the one to bring it down?"
"But you have no choice," says Chibi-Chibi. "There is no alternative. To bring peace to the galaxy, there is nothing else..."
"But even if this galaxy is destroyed," says Galaxia, "somewhere a new Cauldron will surely be born again. Somewhere a new future will begin, and light and darkness may be born again. The end of war will not come so easily. A new future... Amazing, that those words are still inside me."
"Yes," says Usagi. "Yes. New futures will always continue to be created. And there, light and darkness, war and hope, life and death, joy and pain, will all exist again. Everything, that is this universe."
"Sailor Moon...!" thinks Galaxia. "You believe in such a distant future for this universe? Sailor Moon, are you the soldier that draws in everything? Sailor Moon... I've finally found it. My planet..."
At this point, Galaxia's bracelets break and she dies but not without saying that 'that planet will shine ternally' (meaning Usagi)
Usagi holds it (the bracelets) in her hands as tears fall from her eyes.
"Chibi-Chibi," she says. "I won't give up. Everyone always told me... At the end of war there is hope and future. I will make our future. So don't you abandon hope and the future, either. Believe. Our star of hope will never disappear. As long as it keeps shining, we will be all right. We won't be defeated."
"Right," says Chibi-Chibi. Light glows around her. She transforms, becoming older. She floats up in her glowing adult body, and kisses Usagi. A spark of light shines on her forehead. (she has now transformed in Sailor Cosmos)
Their hands touch.
At this point, with renewed courage and strength, Usagi descends into the cauldron herself to save her friends, her lover, and her daughter.
Outside of the cauldron, Chibi/Chibi Cosmos stands and speaks to the Sailor Quartet (Chibi Usa/Rini's future guardian senshi/soldiers)
The woman in a sailor suit and cape, two long ponytails flowing over her shoulders, a light sparkling on her forehead, stands before them.
"I am Sailor Cosmos."
"Sailor Cosmos!?" says Ceres. "It can't be... It can't be... Are you the future... The future Sailor Moon's ultimate form!?"
"I am only a coward," the woman says. "I abandoned everything, and ran away from where I should have been. Eternally, I am no match for the final courage and strength of Eternal Sailor Moon."
"Final courage!? Then, is Sailor Moon-!? She can't be..."
"Sailor Cosmos! Our princess...!" (they are asking about Chibi Usa, she is the Princess now because in the manga Sailor Moon/Usagi is the Queen and no longer just a princess)
"Do not worry," she says. "Your princess, the same as the other soldiers, was reborn by that Lambda Power. Someday, in that flow of lights, she will arrive safely back in the 30th century. This is the Galaxy Cauldron. Where the galaxy's stars are born, and where they finally return. To engage the source of all the enemies who inhabited here, Chaos, Eternal Sailor Moon melted along with Chaos into the Cauldron's sea of origin. Not the power of Eternal Sailor Moon, but the Cauldron, and the galaxy, were able to return everyone. But in the end, they could not completely eliminate Chaos."
Memories echo in her mind.
"From an overwhelming future, where I lost the war to Sailor Chaos, I gave up everything and ran away. Repeated massacres, a long, painful war... The enemy that appeared, the strong, enormous Sailor Chaos... With the way of fighting we had used, we didn't stand a chance. Even if we defeated it, even if we returned the peace of before, the damage taken, the price we paid, would be too much. Too far-reaching. We couldn't do it. I don't know anymore, why there are wars. What is right. What should I do? When I'm lost, when I'm hurt, I remember. The war here. Back then at the Cauldron. If I had eliminated it, would the pain, would the war have ended? After regretting it so many times, I came here. To make it right this time."
*Flashback*A small girl floats down from above, holding an umbrella over her head. *This is Chibi Chibi - End of Flashback*
"The me of here, too, (Usagi because of Mamoru's death) 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.... But I knew. The chosen path was not a mistake. Nobody can destroy the place where stars are born. Because of this place, we can continue living. Time and time again, we can start over. I won't run away anymore. I'll go ahead to the future. 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!"
"Now Eternal Sailor Moon, who saved the galaxy, is the true Sailor Cosmos. When, like Eternal Sailor Moon, I can have the courage to stand alone, and the courage to accept everything, at that time I can be the true Sailor Cosmos. Now, you shall return as well! To the place where you must return, to the person you must protect!"
She raises her scepter, and the Sailor Quartet are transformed into lights, joining the others.
Alone, she watches as they go.
From here, all we know is that she returns to the future, to battle Chaos there. Perhaps Naoko will contnue the series and we will learn of what happens in the future. But everything above is all we know of the final reincarnation of Sailor Moon/Chibi Chibi/Cosmos.
Please educate people now that you know both the anime and manga truths of who Chibi Chibi is. Please let them know who Chibi Chibi and Cosmos really are - the light of hope and salvation, the Messiah, Sailor Moon, our beloved Tsukino Usagi (serena) :)