Ail and Ann were aliens that landed on earth that were lovers. With them, they brought a tree called The Doom Tree. This tree gave them energy so they would survive. But in order for the Tree to survive, they had to feed it energy from humans. They used monsters called "cardians" to gather energy.
They posed as brother and sister named Seijuurou and Natsumi Ginga at Usagi's School. Ail fell in love Usagi, and Ann fell in love with Mamoru, which set back their plans of collecting energy for the Doom Tree. They turned to the side of good when Sailor Moon revived the Doom Tree with her "Moon Princess Halation" Attack.
