Ail and An were created especially for the anime, they never appeared in the manga. They were so-called "filler" villains, so that the manga could catch up. Ail and An first appeared on Earth to gather energy to feed the Makaiju, the tree that sustained their lives. They arrived on Earth when a comet crashed into Tokyo leaving a big crater. They decided to save their dying tree by draining the energy from humans by using monsters called Cardigans. They posed as brother and sister and enrolled at Usagi's Junior High. At the end, they are healed by Sailor Moon and go off into space.

Eil (Allen in N.A)
His alias is Ginga Seijuurou. When he first started at Juuban Jr. High, all the girls had mad crushes on him, even Usagi. He has a talent for playing the flute. He lets An pick a card, and then he plays his flute to call forth the Cardigan. He immediately falls in love with Usagi, although he loves An very much. This makes An very jealous. During their battle with Sailor Moon, he tries to destroy Mamoru. He then begins to question their ways. He starts to believe that what they are doing is wrong.

An
Her alias is Ginga Natsumi. She is very rude and mean. She has a very bad attitude and is always very mean to Usagi. She is jealous of Usagi, because of Eil's love for her. She falls in love with Mamoru, which makes Eil very jealous. She has no friends because of how mean she is. She picks the Cardigan for Eil. She dies while trying to destroy Usagi but ends up getting hit by one of the Makaiju's tentacles. She is resurrected after Sailor Moon heals the Makaiju. She and Eil then float off into space with a Makaiju sappling.

The Makaiju (Doom Tree in N.A.)
Makaiju means Tree of Hell or Hell Tree. It was the tree that keeps Ail and An alive. They try to feed it negative energy and it tends to get better and then wither. After An dies, the Makaiju starts to cry, and then reveals that it is, in fact, conscious. It then tells a story of how a long time ago it lived alone on a water-planet. It didn't want to be alone any more. Therefore it created its children. At the beginning they lived peacefully together but than they started to fight and to kill each other. They destroyed their world. Only few of them survived and together, with the tree, they travelled through the universe in search of a new home. All of the tree' s children died except for Eil and An. They had been alone almost all of their lives, so they never knew what love was. It reveals that when it sensed Sailor Moon's prescence, it began to awaken from the long sleep it was in. It reveals that it really lives on love energy. It then asks her to purify it since it is decaying from the anger within it. Sailor Moon uses her princess halation, and with it's last act, it heals Ann. Then Ail and An are given a sappling to take off into space with them.