TV series
Kate, Rachel, Rose, and Claire are all students at a private school set on Roosevelt Island, New York City. Waking up one morning, all feel uneasy and restless as they deem strange that none of them can recall anything about the previous night. Their anxiety escalates when the school announces that Lise, another classmate of theirs and friend to all four girls, is found dead.
The following night the four girls are drawn by butterflies that lead them all to the same place. There, they are approached by a woman called Lula and her partner JC who tell them that they are dead, and must work for them. They are revealed to be working for an organization called Animus. On certain nights the girls are summoned to fight "monsters" that look almost like regular people, and can do this by using superhuman abilities. After a fight the girls are drained and tired. If they fail, they will die for real, like other girls who work for Animus. Later Lulu explains the girls were reanimated in new, special bodies and their real bodies are in her custody. What's more, when Lise had originally disappeared, the girls had gone looking for her, and right after they found her dead body was when they were killed. Lise was also supposed to have been reanimated, but the "monsters" had prevented this. Lula further claims she has the means to eventually return the girls to their previous lives when their job is done.
The four girls are involved in a centuries-old battle between the Animus and the Dolore clans. Long ago one of a pair of a Book of Curses was stolen by the Dolore, and because of that they were put under a curse where they become beasts and die, while the Animus lost their freedom and were cursed with eternal life. The Animus want to retrieve the stolen book that is now held by the Dolore and the Dolore want the other book now held by the Animus.
Meanwhile, Hervé of the Dolore clan is trying to save the lives of his cousin and sister, as they are subject to the curse. To do this he plans to take the companion book from the Animus clan. The four girls find out if they fail to retrieve the book from the Dolore family it will result in them losing their memories. This means that they would live forever but not remember their friends or family.
A considerable portion of the series is devoted to the effects that these events have on the girls' complex personal lives: While they overcome their obstacles by eventually agreeing to support each other, the series explores both their initial individual struggles in coming to terms with their roles as fighters for the Animus, and balancing these roles and their relationships with family and friends.
OVA
Set 300 years in the future, Kate, Rose, Rachel and Claire have no memory of their first 17 years, but know that the Red Garden on Roosevelt Island holds the key. They divide their immortal lives between normal school life and vigilantism. Then two mysterious transfer students Louise and Edgar Mayer seek out their friendship.
The girls go to explore the Red Garden but are attacked by a giant robot. Rachel constructs a very stylish and fashionable robot herself, and the girls return to the Red Garden. They are again attacked by a more powerful mechanical device controlled by Edgar Mayer but manage to defeat it. Louise appears and is revealed to be a powerful android, who envies the 'Dead Girls' because they live forever. Before she can attack the girls, the island's vegetation comes alive and envelops her and Edgar. After graduation, the girls decide to move on, planning to return in a couple of hundred years.
