Once upon a time, there was an era of the Moon Kingdom called the Silver Millennium, ruled by Queen Serenity. Her daughter was Princess Serena, the future ruler of the kingdom. She had four protectors: Sailor Mercury, Sailor Mars, Sailor Jupiter, and Sailor Venus.
Princess Serena had fallen in love with the prince of Earth, Prince Darien. Although they loved each other, they were forbidden to see each other. One night, during a ball at the palace, he came to see her in secret. As they were standing on a balcony, something arrived. Something bad. It was the Nega-verse. The Nega-verse lived on the Dark Side of the Moon, and was ruled by Queen Metallia.
She sent her strongest soldiers, the 7 rainbow warriors, to attack everyone and everything. As Darien was lifted off the ground into the air, Serena jumped after him and grabbed his hand, both of them being killed. Queen Serenity wanted her daughter and the others to be reborn again, so she used the last of her strength to send all her people to Earth, where they would be reborn and know nothing.