Sailor Moon (美少女戦士セーラームーン, Bishōjo Senshi Sērā Mūn; officially translated as Pretty Soldier Sailor Moon) is the title of a Japanese media franchise created by Naoko Takeuchi. Fred Patten credits Takeuchi with popularizing the concept of a sentai ("team") of magical girls, and Paul Gravett credits the series with "revitalizing" the magical girl genre itself. Sailor Moon redefined the magical girl genre, as previous magical girls did not use their powers to fight evil, but this is now considered one of the standard archetypes of the genre.
Before the Sailor Moon manga appeared Takeuchi had written Codename: Sailor V, which centered around just one Sailor Senshi. She devised the idea when she wanted to create a cute series about girls in outer space, and her editor asked her to put them in sailor fuku. When Sailor V was proposed for adaptation into an anime, the concept was modified so that Sailor V herself became only one member of a team. The resulting manga series merged elements of the popular magical girl genre and the Super Sentai Series which Takeuchi admired, making Sailor Moon one of the first series ever to combine the two.
The manga resulted in spinoffs into other types of media, including a highly popular anime, as well as musical theater productions, video games, and a tokusatsu series. Although most concepts in the many versions overlap, often notable differences occur, and thus continuity between the different formats remains limited.
The protagonist of Sailor Moon, Usagi Tsukino, an ordinary ditzy middle-school girl - or so she herself thinks, at least - discovers a talking cat named Luna, who reveals Usagi's identity as "Sailor Moon" a special warrior whose destiny it is to save the planet Earth, and later the entire galaxy. Supposedly, Usagi is the reincarnation of the Moon Princess. Now, Usagi must protect Earth from a series of bad guys, beginning with a Dark Kingdom that had appeared once before, long ago, and destroyed the kingdom of the moon. Usagi's dormant powers are then awakened (under Luna's guidance) to defend the Earth against the coming onslaught.
The characters in Sailor Moon reincarnate members of the court of the kingdom of the moon, and the people dedicated to protecting it. When the kingdom was attacked by the dark nemesis, the Queen sent the Moon Princess, her guardians and advisers, and her true love, into the future to be reborn. As Usagi and Luna battle evil and search for the Moon Princess, they meet the other Sailor Senshi, incarnations of the Moon Princess' protectors, and the mysterious Tuxedo Mask.
As the series progresses, Usagi and her friends learn more and more about the enemies they face and the evil force that directs them. The characters' pasts are mysterious and hidden even to them, and much of the early series is devoted to discovering their true identities and pasts. Luna, who teaches and guides the Sailor Senshi, doesn't know everything about their histories either, and the Senshi eventually learn that Usagi is the real Moon Princess. The Moon Princess' mother had her reborn as a Sailor Senshi to protect her. Gradually she discovers the truth about her own past life, her destined true love, and the possibilities for the future of the Solar System and herself.