Chibiusa is the future daughter of Usagi and Mamoru. She lives in the 30th century Crystal Tokyo and is called Small Lady up until the day the family of Nemesis attacked. She was sent back in time to the 20th century to find the ginzuishou because the one kept in the Crystal Palace mysteriously disappeared. She lands on Usagi's head while she and Mamoru are kissing in the park and demands Usagi to give her the ginzuishou. She immediately forms a crush on Mamoru and makes Usagi very jealous when Mamoru pays attention to her. Only near the end of SailormoonR do they all find out Chibiusa is Mamoru and Usagi's daughter from the future. Soon after, Wiseman tricks Chibiusa into thinking no one loves her and her happy memories were just an illusion; she then gains the power of the black crystal and becomes Black Lady. Sailormoon shows her that she is loved, however, and she becomes the sweet (yeah right) little girl she once was. At the end of SailormoonR, Chibiusa returns to the future, but is sent back in SailormoonS to train as a sailor soldier, Sailorchibimoon! She refers to herelf as the "pretty soldier in training".
In SailormoonS, Chibiusa makes friends with a lonely girl named Tomoe Hotaru, who later eats her pure heart crystal to become Mistress Nine (and Setsuna has a cow ^_^). Hotaru defeats Mistress Nine, however, and returns Chibiusa's crystal and all is forgiven.
Later, in SuperS, Chibiusa meets Pegasus, a winged horse also known as Helios (the unicorn boy! hehe...), and they fall in love. Chibiusa is the carrier of the Golden Mirror, which the Dead Moon Circus is after because Pegasus lives in her beautiful dreams, and they are after his golden horn. Pegasus powers up Sailorchibimoon, and she can now become SuperSailorchibimoon. In one famous SuperS episode, ParaPara switched Sailormoon and Sailorchibimoon's ages. When the other soldiers see Sailorchibimoon, they think she's turned into Black Lady again!
Chibiusa also gets a Guardian Cat named Diana. Diana is the daughter of Luna and Artemis in the future and is very kawaii! She likes FishEye and always comments on his smell. FishEye freaks out when he sees Diana though.