Sailor Mercury was one of Princess Serenity's guardians, and was the first Sailor Senshi to join Sailor Moon in her fight. Her current incarnation was Ami Mizuno, and her powers were derived from water. Her sharp mind and analytical abilities made her the strategist of the Inner Senshi.

Depending on the continuity, she referred to herself as the "Soldier of Water and Intellect" or the "Soldier of Knowledge," under the guardianship of the "Planet of Water" (the literal meaning of the Japanese name for Mercury).


In the anime, the Sailor Mercury who lived during the time of the Silver Millennium was responsible for protecting Princess Serenity along with Sailor Mars, Sailor Jupiter, and Sailor Venus. All four guardians were killed by Queen Metalia during the Dark Kingdom's surprise attack on the Moon. Queen Serenity then sent the fallen Senshi into the future to be reincarnated.

Sailor Mercury was reincarnated on Earth as Ami Mizuno. Although her Senshi powers were not supposed to have been reactivated, this became necessary after the Dark Kingdom were found to have been reincarnated as well. Sailor Mercury was the third of the Sailor Team to awaken, and the second to be awakened by Luna.
Eventually, the Dark Kingdom's base was located at D Point. By now, the Sailor Team had recovered their memories of their past lives, and were determined to prevent a repeat of Metalia's devastating attack. However, they were confronted outside the base by the DD Girls, five extremely powerful Youma who proceeded to decimate the Sailor Team. Sailor Mercury was killed by three of the DD Girls, although she succeeded in depriving their leader of her ability to create illusions.

Only Sailor Moon survived the battle, but the spirits of Sailor Mercury and the others joined her as she battled Super Beryl. As Metalia was finally destroyed, Sailor Moon wished for herself and her friends to be returned to their old lives. The Silver Crystal acted upon this wish, resurrecting the Sailor Team and Mamoru, and returning them to Azabu-Juuban with no memories of their lives as Sailor Senshi. Only Luna and Artemis retained memories of what had transpired.
The peace did not last long, however, and Luna and Artemis were soon forced to reawaken the Sailor Team due to the activities of Ail and An. Sailor Mercury and the others had their memories restored and regained their powers.

When Sailor Moon and Sailor Chibi Moon were trapped by Fisheye during the battle with the Dead Moon, Pegasus granted extra power to the Sailor Team, allowing them to achieve their "Super" forms. Sailor Mercury's Star Power Stick became a Crystal Change Rod, which allowed her to transform from Ami Mizuno directly into Super Sailor Mercury.
Sailor Mercury, along with the rest of the Sailor Team, had her Star Seed removed during the face off with Sailor Galaxia, causing her to lose her physical form and effectively rendering her dead. Fortunately, her Star Seed was released after Chaos was expelled from Galaxia, and Sailor Mercury was brought back to life.