The protagonist of Sailor Moon is Usagi Tsukino, who lives as an ordinary middle school girl until she is found by a talking cat named Luna. Through Luna, Usagi learns that the world is about to be attacked by a Dark Kingdom that had appeared once before, long ago, and destroyed the kingdom of the moon. Her dormant powers are then awakened to defend the Earth against the coming onslaught, and she is led to a number of friends who join her in the battle.
Usagi fights using the identity of Sailor Moon, and as the story progresses she learns more and more about the enemies which face her and the evil force that is sending them. Gradually she discovers the truth about her own past life, her destined true love, and the possibilities for the future of the Solar System.
The plot spans five major story arcs, each of which is represented in both the manga and anime, usually under different names. These are the Dark Kingdom arc, the Black Moon arc (Sailor Moon R), the Infinity arc (Sailor Moon S), the Dream arc (Sailor Moon Supers), and the Stars arc (Sailor Stars). The anime added an additional minor arc at the start of the second series, and spent the first few episodes of Sailor Stars wrapping up the plot from the previous series.