"Sailor Moon" centers on Usagi Tsukino, a clumsy but kind-hearted teenage girl who discovers she is the reincarnation of a magical warrior, Sailor Moon. Tasked with protecting Earth from evil forces, Usagi transforms into Sailor Moon with the help of a talking cat named Luna, who serves as her guide. The series begins with Usagi encountering Luna, who reveals her destiny to fight against the Dark Kingdom, a malevolent group seeking to drain Earth's energy and resurrect their queen, Queen Metalia.

As the story progresses, Usagi is joined by other Sailor Guardians, each representing a celestial body and possessing unique powers. These include Ami Mizuno (Sailor Mercury), Rei Hino (Sailor Mars), Makoto Kino (Sailor Jupiter), and Minako Aino (Sailor Venus). Together, they form a team dedicated to defending Earth and uncovering their shared past as warriors from the ancient Moon Kingdom. The group faces various antagonists, including members of the Dark Kingdom, such as Queen Beryl and her generals, who seek to exploit the Guardians' weaknesses.

The narrative explores themes of friendship, love, and self-discovery, as the Sailor Guardians balance their ordinary lives with their duties as protectors. A central romantic subplot involves Usagi's relationship with Mamoru Chiba, also known as Tuxedo Mask, a mysterious ally who shares a deep connection with her. Their bond is tied to their past lives as Princess Serenity and Prince Endymion, rulers of the Moon Kingdom and Earth, respectively.

Throughout the series, the Sailor Guardians confront increasingly powerful enemies, including the Black Moon Clan, the Death Busters, and the Shadow Galactica. Each arc introduces new allies, such as Chibiusa, the future daughter of Usagi and Mamoru, and additional Sailor Guardians representing outer planets, like Sailor Uranus, Sailor Neptune, Sailor Pluto, and Sailor Saturn. The overarching plot reveals the Guardians' ultimate mission to protect the Silver Crystal, a powerful artifact tied to the fate of the universe.

The series blends action, comedy, and drama, with a focus on the personal growth of its characters. Usagi evolves from a reluctant hero into a confident leader, while her friends confront their own insecurities and challenges. The narrative emphasizes the importance of unity and perseverance in the face of adversity, culminating in epic battles against cosmic threats that test the Guardians' resolve and strength.