Usagi and Mamoru will rule it under the names of Neo-Queen Serenity and King Endymion, and they will have a daughter named Princess Usagi Small Lady Serenity. The Earth becomes a world wide kingdom once again.
The Guardian Senshi protect the entire royal family. Sailor Pluto guards the space-time door. At the center of the kingdom stands the Crystal Palace, where the Royal Family and the Guardian Senshi live. Luna, Artemis, and Diana live in the palace as well.
Exposure to the Silver Crystal renders all of Earth's inhabitants functionally immortal. Anyone not born in Crystal Tokyo becomes essentially locked at their current physical age, as shown by the Queen and King Endymion and the Guardian Senshi court, who all appear as if aged in their early twenties. Anyone born in Crystal Tokyo has a slow growth-rate.
There was a sudden unbelievably big explosion in Crystal Tokyo and everyone except Chibiusa collapsed.