Ami Mizuno is the civilian identity of Sailor Mercury.
She has short blue hair and blue eyes. She wears her school uniform, with a grey cardigan, white socks, brown penny loafers and blue stud earrings.
She is a fourteen year old eighth grader who's a student at Juuban Municipal Junior High School in class 5 and attend Crystal Seminar every evening. Ami is smart, she receives 100% on tests. She wants to be a doctor like her mother. She is shy and doesn't have any friends, until she meets Usagi Tsukino. Usagi describes Ami as a kind-hearted genius girl with an IQ of 300.
Act 1 - Ami is seen from above walking in the school yard, and as it begins to rain she starts running.
Act 2 - When Usagi sees Luna with Ami, she decides to go talk to Ami, only to discover she's not cold and distant, she is shy. As Usagi takes Luna from Ami they brush hands and Ami receives a flash of the Moon Kingdom.
Usagi invites Ami to go to the arcade, while there Usagi introduces Ami to Motoki Furuhata. Usagi and Motoki are impressed by Ami's video gaming skills. Ami draws a crowd, she beats the high score and wins a prize in the form of a pen. When Ami realises how late it is, has to leave to attend the cram school Crystal Seminar, which is located just around the corner from the arcade.
While at Crystal Seminar Ami's teacher gives her a computer disk to study and instructs her to use it everyday so she can be a role model to other students.
The next day at school, while in the library Usagi invites Ami to join Naru, Yumiko and herself for ice cream. At first Ami reply's yes but then declines because she needs to study.
Ami's teacher pushes a hypnotised Ami to work harder and faster on a computer disk especially designed for her. When her teacher sees Ami's pen, she considers it a distraction and throws it away so Ami can focus on her work.
When Sailor Moon yells for help, the Planetary Symbol for Mercury glows on Ami's forehead. Luna tells Ami she is a Sailor Guardian and to use her pen to transform. Ami calls out the phrase Mercury Power, Make Up and transforms into Sailor Mercury.
After the fight Ami wants to learn everything she can about being a Sailor Guardian from Usagi, so they decide to have a meeting so they can review the events that have just taken place.
Act 3 - Ami and Usagi meet at the arcade. Luna explains their mission is to find and protect the Princess and the Silver Crystal. When Ami has to go to Crystal Seminar, Usagi follows her onto the bus so she can get a glimpse of a beautiful girl Ami sees often on the bus.
The next day while at school, Usagi gives one of the watches - which turn out to be communicators - she received from the Sailor V video game machine to Ami and keeps the other for herself. Luna reveals Rei Hino could be the Princess they are searching for.
After Usagi has vanished on the demon bus, Luna contacts Ami in order to track Usagi's whereabouts. When Ami tries to track Usagi's location using her miniature super computer and Usagi's new communicator, she discovers the signal is too weak. Ami contacts Usagi to transform so then she as Sailor Mercury will be able to teleport directly to Sailor Moon's location, so Usagi transforms.
Act 4 - Ami meets Rei at the arcade. While they wait for Usagi to arrive so they can start their Sailor Guardian meeting, they play Sailor V video games.
Usagi uses her disguise power to change in a princess to attend Princess D's masquerade ball at the embassy with Luna, Ami and Rei. While Usagi goes to the main ballroom, Ami and Rei search for Princess D. Ami and Rei witness Princess D enter a room on the second floor of the building with an Attendant and barge into the room. The Attendant changes into Nephrite and sends a shadow spectre into Princess D, possessing her in order to steal her treasure, so Ami and Rei transform.
Act 5 - After Ami arrives at the arcade, Motoki informs Usagi, Ami and Makoto Kino of a rumour he heard from a customer so they go to the Bridal Shop and talk wedding dresses. Ami would prefer a pure white kimono over the traditional wedding gown.
Act 6 - While walking to school with Ami and Makoto, Usagi bumps into Mamoru. A report on TV discloses Tuxedo Mask issuing a statement to the media claiming that he has been committing crimes in order to obtain a lost treasure known as the Legendary Silver Crystal said to be somewhere in Japan.
Usagi, Ami, Rei and Makoto meet Luna at the arcade where Luna informs them of her mission to awaken the Sailor Guardians. After Usagi arrives home to find her mother hypnotised and frantically searching for the Silver Crystal, Luna contacts the other girls who are out on the street witnessing other hypnotised humans search for the Silver Crystal. They all meet up at the arcade again when there Luna shows them their secret headquarters where she has been doing research on the enemy. Ami suspects the enemy is sending signals from the TV station to control people's minds. After Usagi leaves, Ami, Rei, Mako and Luna head to the TV station where Dr. Isono reveals herself to be Zoisite so the girls transform.
Act 7 - Ami does research on Sailor Venus. When Usagi, Ami and Makoto are having lunch at school, Umino jumps out from behind the bushes acting creepy, he announces Sailor V is out and Sailor Moon is in now. When Ami questions if Luna knows anything about Sailor Venus, Luna denies knowing anything.
While at the arcade Usagi, Ami and Luna place a DVD from Rental Shop Dark into a machine. When played there's static and the machine spits the disc out. The Sailor V video game character comes on the machine and tells them it's the enemy's DVD meant to brainwash everyone who watches it, they are all over town and people's lives are in danger. While Usagi goes to help the people, Ami investigates the DVD further to see what she can find out.
Ami discovers the DVD brainwashing program contains a message from Zoisite announcing that Sailor Moon holds the secret to the Silver Crystal and she must be sacrificed to the Dark Kingdom. Ami contacts Rei and Makoto believing Usagi is in danger, they set out to find her after they transform.
The next day when Minako runs into Usagi, Ami, Rei and Makoto on her way to fight Kunzite alone at Tokyo Tower, the girls invite her to dinner at Makoto's Apartment. After Kunzite blacks out the entire city, Luna contacts the girls via Usagi's communicator so they can transform and investigate.
Act 9 - When Ami, Rei, Makoto, Minako, Luna and Artemis arrive to cheer up Usagi, Ikuko Tsukino lets them know she hasn't come out of her room in a while. When they enter Usagi's room, they are shocked to see her hair. Ami brushes Usagi's hair.
Act 10 - At the arcade Usagi, Ami, Rei, Makoto and Minako discuss going to the moon so they can unearth all its secrets. That night Ami meets the other girls and Luna at the park so they can travel to the moon while it is full. Once Luna makes a beam that will take them to the moon, the team step into the fountain and transform.
The next day at HQ Luna discovers that the movement of the Earth's crust has been more active recently, Artemis adds that there's an unusual thermal reaction around the North Pole, so the Sailor Guardians transform in order to investigate.
Act 11 - Usagi, Rei, Makoto and Minako walk to Ami's home for a sleepover. Ami places a diamond ring on the table and has Minako hit it with the Sacred Sword which shatters the diamond. Ami concludes both the sword and rock fragments they brought back from the moon are composed of very strong unknown elements but are both solid and poisonous.
Makoto contacts the team a states there is an emergency at HQ. The HQ alarm sounds to alert them to an intruder inside HQ. That's when they notice Tuxedo Mask and Motoki are inside HQ, so Ami transforms into Sailor Mercury.
Act 15 - Usagi, Ami, Rei, Makoto and Minako discuss Chibiusa Tsukino at the Fruits Parlor Crown while eating sundaes. Luna arrives with new transformation pens for the Inner Senshi and communicators for all five girls.
The next day when Usagi, Ami, Makoto and Minako arrive at T-A Academy for Girls, Rei informs them they have a new enemy. Ami uses her Star Power Stick and calls out the phrase Mercury Star Power, Make Up to transform into a stronger version of Sailor Mercury.
Act 16 - Luna contacts HQ where Ami, Makoto, Minako and Artemis are to inform them what she has learnt about Chibiusa. Ami plays chess against the computer.
When taps run dry at school Ami believes it could be the pipes. She listens carefully to the sound of the water, hearing it's ripples and feeling it's flow to pinpoint the disruption. When she discovers where the broken water pipes are, Ami tells the School Janitor. Berthier appears to ridicule the method in which Ami found the problem.
Ami goes swimming at the Health Club where her father is a member and run into Naru and Usagi. When they get out of the pool they see an interview on TV where Berthier challenges junior chess champion Ami to an individual chess match, which she accepts.
Ami makes a deal with Berthier that whoever captures the others king gets whatever she wants. If Ami was to win Berthier would return Sailor Mars and if Berthier was to win she would get Chibiusa. Ami realises the Black Moon Clan are after Chibiusa. Throughout the match Berthier distracts Ami by taunting her which makes Ami recall when she was young and her father left. Ami gets slightly upset and unfocused. Usagi encourages Ami by calling out from the audience which makes Ami remember all the good times, she re-focuses which makes Berthier angry and Ami wins the match. When Ami demands she return Sailor Mars, Berthier takes the fight outside. The security guards change into Droids and Ami transforms into Sailor Mercury.
Act 21 - Ami awakens in the Darkness Chamber on Nemesis with Rei and Makoto after hearing Usagi's voice in her head. They are unsure what broke their transformations, where they are and for how long they've been there for. When Makoto suggests they transform, Ami calls out Mercury Star Power, Make Up but they are unable to use their powers. All of a sudden they can't breath and begin losing energy.
Act 22 - Sailor Moon sends her excess power to Ami, Rei and Makoto. They are now able to transform with a hand from Sailor Moon.
Act 23 - Usagi wakes-up back in her room in the 21st century with Ami, Rei, Makoto, Minako and her mother standing over her. Ami and the other girls are just as eager as Usagi to find Mamoru and Chibiusa. After the girls leave Usagi's house, a shock-wave from the 30th century is felt in the 21st Century, the girls return to check if Usagi is alright. Knowing something is wrong in the future the girls transform.
Act 27 Part 1 - Ami was able to read an entire book while waiting for Usagi to arrive at the arcade. Ami recognises the school uniform Haruka Tenou was wearing is from Mugen Academy. As Usagi, Ami, Rei, Makoto, Minako, Naru and Mamoru are walking down the street, Umino suddenly appears from out of nowhere. When a Daimon appears, Ami calls out Mercury Planet Power, Make Up! for the first time to transform.
After the fight Usagi, Ami, Rei, Makoto, Minako, Mamoru, Luna and Artemis meet at HQ to discuss recent events seen to be surrounded around Mugen Academy. Everyone agrees with Minako when she announces they will have to investigate Mugen Academy as soon as possible.
Act 27 Part 2 - Usagi, Ami, Rei, Makoto and Minako investigate Mugan Academy. Ami notices the whole area doesn't have the right spatial density, it's distorted. After Usagi uses her Disguise Pen and enters the school alone, Haruka warns Ami, Rei, Makoto and Minako not to poke around. When a Daimon attacks Usagi and Chibiusa, Ami, Rei, Makoto and Minako hear their screams and come running. Unbeknown to them, as all 6 transform they are watched by Sailor Neptune, Sailor Uranus and Hotaru Tomoe.
Act 28 - Usagi, Ami, Rei, Makoto, Minako, Mamoru and Chibiusa meet at HQ where Luna and Artemis have been analysis the two unknown Sailor Guardians.
While at the Fruits Parlor Crown Cafe, Makoto tells Usagi, Ami, Chibiusa and Minako how excited she is for Rei's upcoming birthday. When Minako informs Makoto that Rei is training in the mountains they decide to surprise Rei.
Usagi, Ami, Makoto and Minako surprise Rei and throw her a birthday party. Makoto baked a cake, Minako brought Casa Blanca Lilies, Usagi brought a tea set and Ami got Rei the workbook "Highest Level Workbook for Third-Year Middle School Students" to help prepare for exams. The girls check out a Gymnasium in a nearby building owned by Mugen Academy where students are practising judo. When Eudial arrives the girls run off because they're not supposed to be there.