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 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 the Earth stopped ageing and began to enjoy longevity with lifespans of around 1,000 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 presumed 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 awakens the planet with the Silver Crystal, and with her as the Queen, the Earth prospers around the future utopian city.
There is peace for some time, but darkness grows again. King Endymion and Neo-Queen Serenity fight against the evil beings and suppress them, but those that did not want to be cleansed left Earth. The city and Earth continues to prosper until the attack by the Black Moon Clan from Nemesis. In the battle, the entire Earth falls into silence and the city is the only stronghold remaining. King Endymion is badly injured in the battle and subsequently, can only appear as a holographic image. Sailor Mars, Sailor Venus, Sailor Jupiter, and Sailor Mars continue using their powers to guard the city but the only power that can save the city is the Silver Crystal. Unfortunately, the only one who can use it, Neo-Queen Serenity, is in an unshakable deep sleep, wrapped in crystal provided by her guardians at the moment of a direct attack from the enemy.
The city forms the shape of a five-pointed star when seen from above. The five locations which form the points of that star are known as Crystal Points. Various members of the Black Moon Clan tried to take control of those points in the past on Earth in order to prevent Crystal Tokyo from existing in the future.