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 Earth. It became not only the capital of Japan, but also of the entire Earth. It was a utopia, the epicentre of the new Silver Millennium, at the center of which stood the Crystal Palace.
Crystal Tokyo 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 Earth stoped ageing and began to enjoy longevity with lifespans of around 1000 years. This was 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 Venus, Sailor Jupiter, 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 speculated that Sailor Saturn remained in Crystal Tokyo to be a part of Small Lady's team. It is unclear where Sailor Uranus, Sailor Neptune are at this point. Sailor Pluto is at the Space-Time Door.
Crystal Tokyo in the anime
Sometime after the 20th Century, the Earth undergoes a world-wide freeze for unknown reasons. In the 30th Century, Neo-Queen Serenity revives the planet and clenses the people, forming the utopian city.
In the anime, the city formed the shape of a five-pointed star when seen from above. The five locations which formed the points of that star were known as Crystal Points; various members of the Black Moon Clan tried to take contol of those points in the past on Earth in order to prevent Crystal Tokyo from existing in the future.