Mizuno Ami is very smart, you may say she is the brains of the sailor scouts. She devoted most of her life to studying, and had little friends. When she transferred to Juuban Junior High the other students were jealous of her good grades and did not talk to her. One day Luna got instructions from command control that Ami may be a youma to stop Sailormoon. So Luna followed Ami when she was leaving school that day and jumped out of the bushes onto Ami's shoulders. Luna senses a strange aura surrounding the girl, but gets taken in by Ami's charm. Usagi calls Luna away, as Ami says that she thought the cat was an angel. Usagi introduces herself and thinks to herself that being a friend of a genius might come in handy for tests. Luna whispers to Usagi that she thinks Ami is a youma. Usagi then invites Ami to the arcade. Usagi plays he Sailor V game and dies really early then Ami plays and does very good but suddenly she realizes what time it is and runs of to her cram school. Then Motoki comes up to Usagi and gives her Ami disk and says she dropped it. Usagi says she would bring it right to Ami and leaves the Arcade. Luna says they should check the disk to see what on it. So they return to the school and Luna uses the computer and quickly finds a brainwashing program and then says Ami is the youma. Luna and Usagi return to the cram school and Usagi transform into a nurse using the pen. They storm into the room and yell at everyone to get away from the computers. Ami says she shouldn't interfere in their studies. Usagi transforms and suddenly the teacher appears behind Ami and grabs her and turns into the youma. The youma pushes Ami head against the monitor, asking her to give up her mental energy. But the youma notices that Ami wasn't using the disk and gets mad. Ami retorts that studying was done with ones mind not a disk or a machine. The youma then pushes Ami's head harder against the monitor and suddenly a mark appears on Ami. Luna sees the mark and realizes that Ami is Mercury one of the missing senshi. Luna gets a transformation for pen Ami and slides it towards her and Tells her to say "Mercury power, make up!" Ami does this and she turns into the fighter for love and justice, Sailor Mercury. After Ami and Usagi become good friends and they also learn things from each other, Ami decided to live life more, and Usagi pays more attention in school with help from Ami.

More info on Mizuno Ami

Transformations

Attacks

Ami's Special Mini Computer and Mercury Visor

Also Ami has a mini computer and the Mercury Visor that she uses to find out enemy weaknesses and different stuff. She is the only one to have a mini computer and Mercury Visor. Luna gave it to her in Sailormoon's first season.