The Sailor Scouts are a number of super heroine who protect the earth from the dark forces. Each of the Sailor Scouts are named after the different planets and each are associated with a particular element. The Sailor Scouts are divided into two main groups, the Inner Sailor Scouts and the Outer Sailor Scouts. Each of the Sailor scouts were princess of their own home planet and served the Moon Princess Princess Serenity.

Chibi-usa (Rini in the English dub), is Sailor Mini Moon, a small child from the 30th century who visits the past to seek help from the Sailor Senshi in order to restore her mother Neo-Queen Serenity to normal (she was injured while shielding her from one of the black moon clans dark energy attacks, the queen would've used the silver crystal, but at the time the powerful stone had mysteriously vanished).

Chibi-usa later returns, a few years older, in order to train as a Senshi herself - Sailor Chibi Moon due to her mother's request for her to go back in time to train with her teenaged self so she could learn how to defend the planet properly, and make friends as well.

Chibi-usa is formally named Usagi Small Lady Serenity, but in the 20th century she goes by the name Chibi-usa. She is given her nickname in order to differentiate from the older Usagi Tsukino (Sailor Moon). The nickname is a combination of chibi (meaning runt, dwarf, shrimp) and her given name, Usagi. In her own time period, she is always called Small Lady. In the English-language adaptations, where Usagi had been changed to Serena, the diminutive "Rini" was used for Chibiusa's name.She is the very much loved daughter of Usagi/Serena Tsukino, and Mamoru/Darien Chiba , and the only grandchild of Queen Serenity (the late ruler of the Silver Millienium). She was born in 30th century Crystal Tokyo, where she is the crown Princess. Her full royal name is Small Lady Serenity, in contrast to her mothers former royal name Princess Serenity. As the queen's daughter she is also the heiress to the powerful Silver Crystal which she will use to defend the planet in the distant future.