Disclaimer: I don't own Sailor Moon, natch.

I had this idea while I was staring up at the ceiling in bed, trying to fall asleep. Instead, I sat back up and scribbled this out.

=====

The kneeling, silver haired woman stared in shock at the Ginzuishou cupped in her hands. After becoming Sailor Cosmos and defeating Chaos, she had returned home and prepared to return her friends to life. But, the Ginzuishou couldn't... wouldn't... do as she commanded.

A flash of light startled her out of her brooding.

Floating in front of her was an envelope addressed simply to 'Serenity'.

Cautiously, she reached out and touched the envelope. The touch disrupted the floating spell on the message. She quickly grabbed the envelope before it fell to the ground.

Opening the letter, she recognized Setsuna's handwriting.

=====

Your Highness,

By reading this, you have discovered one of the possible futures I wished would never come to be. You feel too much, too deeply, to loose all of us as you did.

I have written a letter such as this for all the possible timelines I could envision where some, if not all, your Senshi perished permanently. These letters were all written for ones where I am one of those who does not return. As soon as this letter appeared, the others were automatically destroyed. There is no need for you to know of those events, as they can never come to bass now.

You are wondering how this can be? I assured you a bright future called 'Crystal Toyko'.

Crystal Tokyo only had a fifty percent chance of coming to be. The moment you became Sailor Cosmos, that possibility ceased.

I am sorry, my princess.

How could we have saved Crystal Tokyo then? How did Chibi-Usa exist? I had hoped, beyond hoped, that those were not an alternate future for us. You see, every possible outcome of every decision is played out in this big reality we are a part of. In this dimension, you became Cosmos. In the reality Chibi-Usa came from, you did not become Cosmos. The Dark Moon Family followed after her, and so, set those events in motion. So, somewhere, on some plane of existence, Chibi-Usa is alive and well, living with her parents, an alternate version of you and Mamoru, and learning to be a good princess.

You, your majesty, are now the guardian of the Cosmos, Protector of the countless worlds that reside in our reality. For you to become Cosmos, the Senshi must give up their lives and power, permanently.

I know I speak for us all when I state I do so willingly if that means helping my princess, my friend.

You have no doubt noticed you cannot detransform. You are forever now Sailor Cosmos. You can change your outfit with a bit of concentration, but you can never step out of your current role.

I grieve for you, my lady. To be the one being standing between countless horrors and the innocent, never to truly know peace. I am sorry. I did everything in my power to prevent this, but I obviously failed.

My advice, if you wish it, is to leave Earth and travel the cosmos you protect. Travel until the pain dulls some.

And, that doesn't mean standing guard over the Time Gates! For, you truly do not need to.

When I saw that there was only a fifty percent chance of your true happiness, I used everything in my power to make that happiness come to be. I worked diligently for centuries, millennia, nudging events toward our crystal utopia.

But, in this reality, it was not meant to be. I humbly beg your forgiveness for my failure, my princess.

As I was explaining, the Time Gates do not need a full time guard. Lock them closed with the Time Key, and you will not be bound to them. The gates themselves will alert you if someone tries to destroy a timeline, which is the true duty of the guardian of the Gates. To stop the possible timelines from being destroyed.

Also, as the time guardian, you will receive flashes of important events as they happen in your vicinity as well as flashes of the past. Use them well.

I am proud of you, Serenity. You grew into a beautiful woman, both physically an in personality. I wept in joy the day I sensed you reborn, and I now weep for the grief you must now be feeling. I hope this letter has helped some.

I know I and your other Senshi will always be in your heart. And, wherever my spirit may now reside, you will forever be in mine.

Love,
Meiou Setsuna
Sailor Pluto

=====

Tears streaming down her face, she carefully refolded the letter and stared down at it as she thought about her options.

After some quiet contemplation, she agreed with Pluto's advice, to travel the cosmos, her domain.

"I will never forget you, my friends," Sailor Cosmos said. "So says Serenity. No..." A pained look came over her face as she closed her eyes. "I am now Cosmos. No more, no less."

=====

Wow... depressing!

I guess this could be seen as a prequel to my crossover 'Cosmos's New Friends'.