Mizuno Ami is 14 years old, and is Sailormercury.Luna had jumped on her shoulder and noticed a strange aura surrounding her. Usagi invited Ami to play a game, Sailor V, at the Crown Arcade. Ami leaves in a hurry a while later, because she is running late for cram school. As she is leaving, she drops a disk, which Motoki picks up and gives to Usagi. Usagi and Luna check out what's on the disk and discover a brainwashing program, which causes Luna to believe Ami is a youma . They go to the cram school and notice there is trouble. They discover the youma is the teacher, not Ami, and Luna gives Ami her henshin stick . She transformed into Sailormercury.
As the series continues on, Ami's powers increase, and she is able to transform into Super Sailormercury. She learns of her past, as one of Princess Serenity's guardians and as Princess of Mercury.
Ami spends much of her time studying in order to excel at school .She attends Juuban Junior High, and, when she is 16, she attends Juuban High School. Her dream is to be a doctor, like her mother. Her parents are divorced.She lives with her mother and doesn't get to see her father, a painter.