Crystal Tokyo (クリスタル・トーキョー) was the new name given to Tokyo when Neo-Queen Serenity and King Endymion ascended the throne to rule over the Earth. It became not only the capital of Japan, but also of the entire Earth. It was a utopia, the epicenter of the new Silver Millennium, at the center of which stood the Crystal Palace.
Crystal Tokyo in the Manga
In the manga, Crystal Tokyo was formed in the 21st Century when Usagi was 22 years old. When she ascended the throne, the people of the Earth stopped aging and began to enjoy lifespans of around 1,000 years, due to the power of the Silver Crystal. Neo-Queen Serenity watched over the Earth from the Crystal Palace and rarely went outside. Sailor Mercury, Sailor Mars, Sailor Jupiter, Sailor Venus, and Endymion continued to guard Usagi when she became the Queen.
The princess of the new Silver Millennium was Princess "Small Lady" Serenity. Her guardian Senshi, Sailor Juno, Sailor Vesta, Sailor Pallas, and Sailor Ceres were awakened at this time. It is presumed that Sailor Saturn remained in Crystal Tokyo to be a part of Small Lady's team. It is unclear where Sailor Uranus and Sailor Neptune were at this point. Sailor Pluto was at the Space-Time Door.
Crystal Tokyo in the Anime
In the anime, the Earth underwent a world-wide freeze for unknown reasons sometime after the 20th Century. In the 30th Century, Neo-Queen Serenity awoke the planet with the Silver Crystal, and with her as the Queen, the Earth prospered around the future utopian city.
There was peace for some time, but darkness grew again. King Endymion and Neo-Queen Serenity fought against the evil beings and suppressed them, but those who did not want to be cleansed left the Earth. The city and the Earth continued to prosper until the attack by the Black Moon Clan from Nemesis. In the battle, almost the entire Earth fell to the invaders, leaving the city as the only remaining stronghold. King Endymion was badly injured in the battle, and subsequently could only appear as a holographic image. Sailor Mercury, Sailor Mars, Sailor Jupiter, and Sailor Venus continued to use their powers to guard the city, but the only power that could save the city was the Silver Crystal. Unfortunately, the only one who could use it, Neo-Queen Serenity, was in a deep sleep, wrapped in crystal provided by her guardians after a direct attack from the enemy.
The city formed the shape of a five-pointed star when seen from above. The locations which formed the points of that star were known as Crystal Points. Various members of the Black Moon Clan tried to take control of those points in the past on the Earth in order to prevent Crystal Tokyo from existing in the future.