Full Name: Ami Mizuno
Sailor Designation: Sailor Mercury
Weapons: Sailor Star Tamborine, Ice Sword, Mercury Sword
Gear: Silver Bracelet/Jewelry Star Bracelet, TeletiaS, Crown Passport
Attacks: Mercury Aqua Mist, Shine Aqua Illusion, Mercury Aqua Storm, Mercury Aqua Cyclone, Mercury Aqua Blizzard

Ami is exceptionally intelligent, introverted and non-socially apt. She studies hard to become a doctor like her mother. Ami is especially shy and usually wears glasses while in public, even though she does not need them. She had no friends before meeting Usagi and always ate lunch alone on the roof so she can study. When she became Sailor Mercury, Usagi wanted her to be her friend but Ami wasn't sure. The student body felt Ami was stuck up and standoffish for her non-socializing. Usagi seemed to be the only one to see Ami is merely shy, not truly standoffish. Ami initially believed she was being her friend just because she was a Senshi. In Usagi befriending her gradually helps Ami to learn that she is more than just a bookworm. She is extremely loyal to her friends and worries greatly about losing them.

Ami initially had reservations about using Luna's Karaoke Crown Passport to gain free entry, and although Motoki briefly wondered about the existence of these passes, he did not question the Senshi on this matter. Ami was so unused to having friends, that she consulted her old dependable friend: a book. This goes awkwardly wrong. For a short while, Ami and Usagi's best friend Naru share a conflicted relationship as both seem to be jealous of the other's closeness with Usagi. One time when Usagi was under a spell that would turn her into a Youma in Act 14, Ami stood up to Naru to stay out of the way. However, they later resolve their differences and become good friends themselves. In fact in the Final Act when Usagi restored the world but was not present, Ami and Naru were close friends, probably because she knew her true identity.

When the team begins to drift apart, Ami became anxious. Unfortunately, she was caught alone by Kunzite and brought to the Dark Kingdom where she was changed into Dark Mercury by the power of Metalia. The Senshi were unable to bring her back until she injured Usagi and couldn't bear seeing her friend hurt. After being healed, she had no memories of what happened while she was Dark Mercury. This haunts her, as it terrifies her of what she may have done to her friends while not in control. When Nephirite became normal human, he starting working at Crown Karaoke after his forced suicide. He felt the need to return the favor to her from when she was Dark Mercury, a favor which Ami does not recall at the least. Despite this, Ami went out of her way to be kind to him, identifying with feelings of isolation.

Ami has a lonely home life. While her mother is a loving woman and worries about her daughter, she is a very busy doctor and often has overnight shifts. In Act 34, her mother Saeko got a phone call from the police saying that Ami was out late at night, she decided that Ami's new friends may have been a danger to Ami's education and wanted Ami to transfer to a new school. Ami had her first fight with her mother over it, and even ran away from home, spending the night at the Secret Base with Rei. Luckily, Ami convinced her mother that what she's doing in her life right now is more important than studying, she agreed not to transfer schools, because her mother was just looking for her daughter's best interest. Ami's loyalty to Usagi is what allowed her to keep her faith in Usgai's ability to suppress Serenity. And when Serenity finally overcame Usagi's resistance, it is Ami that chose to fight her, because Usagi would have wanted to keep the planet safe. In Special Act, four years had passed and Ami is now studying medicine as the youngest doctor in America. It is expalined that she went to college when everyone else was in high school. She is even seen in a bio-hazard suit and a higher-ranking doctor wants to keep her helping him a secret. She literally hurries to Japan to take care of the threat of Queen Mio and later attends Usagi and Mamoru's wedding.