, better known as , is a fictional character and the titular protagonist of the Sailor Moon franchise created by Naoko Takeuchi. She is introduced in chapter No. 1 of the manga, "Usagi – Sailor Moon" (originally published in Japan's magazine on December 28, 1991), as a carefree Japanese schoolgirl who can transform into the magical "Guardian of Love and Justice", Sailor Moon.

One day, Usagi initially meets Luna, a magical talking black cat who is searching for the Moon Princess. Luna reveals that Usagi is destined to save Earth from the forces of evil and gives her a brooch to transform into Sailor Moon. She asks Usagi to locate the other reincarnated Sailor Guardians, find the princess and protect the "Silver Crystal", an item of immense power. After locating her comrades, Usagi later discovers that she is the reincarnation of the Moon Princess, and that her former lover, Prince Endymion of Earth has also been reincarnated in the present as the mysterious hero, Tuxedo Mask. As Usagi matures, she becomes a powerful warrior and protects her adopted home planet, Earth, from villains who wish to harm it. Usagi is depicted as usually carefree and cheerful, but with immature tendencies that show themselves when things do not go her way.

Usagi appears in every episode, film, video game, and television special of the anime adaptations, Sailor Moon and Sailor Moon Crystal; as well as the live action adaptation, Pretty Guardian Sailor Moon, with her trademark twin buns with twin pigtails. She also cameos in the sister series Codename: Sailor V. She has been the subject of parodies and has appeared in special events. Usagi's critical reception has been largely positive and she is recognized as one of the most important and popular female superheroes of all time, and a cultural symbol of Japan.

Conception and creation Usagi and Sailor Moon series evolved from Naoko Takeuchi's earlier one-shot series called Codename: Sailor V. In Takeuchi's first proposal for the Sailor Moon series, each of the five heroines had a unique outfit. It was eventually decided that they would instead wear uniforms based on a single theme, whose design was closest to Sailor Moon's original costume concept. Sailor Moon's original had some small differences, including color changes, an exposed midriff, and ribbons around the gloves and boots. She also had a mask, which did appear in a few chapters of the manga before being discarded. These aspects of Sailor Moon's costume are shown in multiple pieces of early artwork, along with a gun and cloak, which were also parts of the original concept. (translated by Michelle Bacon of Manga Style)

Of all the Sailor Guardians, Usagi's personality is closest to Takeuchi's own personality at the time Sailor Moon was created. Takeuchi also based Usagi's signature hairstyle on a "good luck charm" she had during her studies as a university student. Takeuchi would put her hair up in odango before difficult classes or exams. Sailor Moon has pink hair in the initial sketches, but by the intermediate stages of development, Takeuchi planned to have the character's hair be blonde in civilian form and change to silver when she transformed. Her editor, Fumio Osano, told her that silver hair would be too plain for cover art. Despite this, stylistic use of differently colored hair does sometimes appear in later artwork, and the concept of the heroines' hair changing color when transformed is used in Pretty Guardian Sailor Moon.

The kanji of Usagi's surname translate as and . Her given name is in hiragana and so its meaning is not inherent, but the word means "rabbit" and this is used as a pun frequently throughout the series, including her hairstyle and possessions. Her name is structured as a pun, as the syllable "no" indicates a possessive, so her name can also be understood as "Rabbit of the Moon". This derives from a Chinese folktale, popular in Japan, about the rabbit which is said to be visible in the Moon's face, much like the Western Man in the Moon. The Mixx/Tokyopop English-language manga – along with other localisations – gives her the nickname "Bunny" to partially preserve this pun. "Usagi" is not a common given name in Japan.

Differences in English and other languages Like other foreign language adaptations, the original North American adaptation of the Sailor Moon anime by DiC and Cloverway took several liberties with the series, changing various aspects and localizing content to fit North American audiences. Among these were renaming Usagi as "Serena", and subsequently referring to Princess Serenity as "Princess Serena." The Sailor Guardians were referred to as "Sailor Scouts" and Sailor Moon's transformations were altered to omit the "Make Up!" phrase. The names of her attacks were also changed. For example, "Moon Tiara Action" was changed to "Moon Tiara Magic", "Moon Healing Escalation" was changed to "Moon Healing Activation" or "Cosmic Moon Power", and "Moon Princess Halation" was changed to "Moon Princess Elimination." In the later seasons, most attacks were maintained according to their original Japanese names and her family name was retained as "Tsukino."

The initial English manga release by Mixx/Tokyopop were made to coincide with the original anime adaptation, so many character names and spellings were kept between the two. However, Usagi's name was changed to "Bunny" to match more closely with her Japanese name's meaning.

Antonia Levi wrote that the two different initial English versions lost some of the meaning behind her name, with the TV version losing the rabbit meaning and the Mixx/Tokyopop name losing the moon meaning.

The initial French, German, and Italian dubs renamed Usagi with rabbit puns. The Cantonese version used the name "Yuet-yeh Toei" (using the characters , ), which Levi stated kept the meaning of the moon and rabbit themes, but "unquestionably changed the heroine's nationality".

Characterization Usagi is first introduced as living the life of a normal teenage schoolgirl in 20th century Tokyo. Although well-meaning, she is an underachieving, accident-prone crybaby. One day, Usagi encounters a mysterious cat with a crescent moon on its forehead, who later reveals herself to be Luna, a mentor archetype who introduces Usagi to her new heroic role. Luna gives Usagi a magical brooch and explains how to use it to transform into Sailor Moon, the Guardian of Love and Justice; she tells Usagi that she is a Sailor Guardian who must fight for peace and find her reincarnated comrades, the Sailor Guardians, to locate and protect their charge, the Moon Princess and the mysterious and powerful Silver Crystal, from the forces of evil. Usagi is a reluctant heroine at first, but grows more confident and mature over time. She eventually discovers that she is the reincarnation of the Moon Princess, Princess Serenity, from the ancient civilization known as Silver Millennium, and the bearer of the Silver Crystal. She also learns that her lover from her past life, Prince Endymion of Earth, has been reincarnated in the present as well as the hero Tuxedo Mask, and seeks to reunite with him. As Sailor Moon, she sets out with her comrades to fight the villains from her past life and to protect the Earth using the legendary Silver Crystal. This provides most of the conflict, romance, and drama in both the manga and the anime.

As a civilian, Usagi lives in Azabu Jūban with her mother, Ikuko Tsukino; her father, Kenji Tsukino; and her brother, Shingo Tsukino; these names reflect those of Naoko Takeuchi's real-life family members. Usagi and her fellow Guardians have diverse backgrounds, and balance their responsibilities as superheroines with their current lives.

Though Tuxedo Mask's identity is initially hidden from her, his civilian identity is eventually revealed to be Mamoru Chiba, who is later revealed to also be the reincarnation of Princess Serenity's star-crossed lover, Prince Endymion. Finally reunited in the present, Usagi and Mamoru become romantically involved. Mamoru and Usagi's relationship is a significant part of Usagi's personal life, as well as the series as a whole. They date for a long time in the series and the love they share helps her through many challenges. In various adaptations of the series, the two eventually marry, and major plot lines involve discovering that she will become a "Sovereign of the Earth", known as Neo-Queen Serenity, by the 30th century, and give birth to her future daughter, Chibiusa.

Usagi is a glutton, particularly for sweet foods and they easily distract her; the manga lists one of her favorite foods as cake. She also loves playing video games and reading manga. Her favorite subject is listed as home economics. She is said to dislike carrots, and is a poor student in both English and mathematics. She is afraid of dentists, ghosts, and thunder and lightning, and her greatest dream is to someday be a bride. She later becomes a member of the Manga Drawing Club at her school, She stands tall, though her height relative to other characters varies from different design models used in various adaptations.

In the manga and anime, Mamoru refers to her as odango (a kind of rice dumpling), based on her distinctive hairstyle. At first, this is always accompanied with the suffix atama, meaning "head", but this is gradually dropped. Usagi hates the name at first, but it develops into a sign of affection as they become close. Later in the series, Haruka Tenō and Kō Seiya, other important figures in her life, adopt the name as well. Since the term does not always have foreign language equivalents, this moniker is altered in various ways across its many foreign translations and adaptations.

Variations Usagi's character is different between versions of the series. In the manga, she starts out as a crybaby, but quickly matures and embraces the responsibilities of her role. Regardless of her maturity as a heroine, the manga often portrays Usagi as lazy or unmotivated in applying herself in her civilian life, such as making fun of her tendency to use phonetic writing instead of more formal script or consistently receiving low academic marks.

The original anime often portrays Usagi as being more childish. She frequently engages in petty squabbles with her friends, usually with Rei, and Chibiusa to the point of developing a friendly rivalry with them or sometimes her little brother Shingo with whom Usagi is not shown getting along and shares a sibling rivalry with. Though she is likewise depicted as deeply caring of those around her, and even of her enemies. Repeated themes in the series depict Usagi feeling sympathy for villains she encounters, and working to help redeem them. Her clumsiness and other slovenly aspects are often highlighted for comedy purposes, both as a civilian and while fighting her enemies. Characters often comment on the unlikeliness of someone with as many graceless qualities like Usagi being a fierce warrior like Sailor Moon, but her lack of grace is simultaneously described as charming to those around her. Usagi's gregarious personality is often emphasized as bringing people together, including her friends and allies.