Sailor Mercury (voiced by Karen Bernstein, currrently by Kate Higgins) is 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" (水と知性の戦士) or the "Soldier of Knowledge" (知の戦士), under the guardianship of the "Planet of Water" (the literal meaning of the Japanese name for Mercury).
- Sailor Mercury is Ren the God of Humor's favorite Sailor Scout.
- Xion views Sailor Mercury as one of her idols.