ONA
Description
Ami Mizuno is a central character in Pretty Guardian Sailor Moon Crystal, where she is known as the civilian identity of Sailor Mercury, the second Sailor Guardian to be introduced. She is a fourteen-year-old student attending Juuban Junior High School, living in the Azabu-Juuban district of Tokyo. Ami resides with her mother, Saeko Mizuno, a respected and busy doctor. Her parents are divorced, and her father, a painter, does not live with them but maintains a distant presence, sending birthday cards. This family background has instilled in Ami a deep respect for the medical profession, and her primary personal dream is to follow in her mother's footsteps to become a doctor.

Ami is distinguished by her exceptional intelligence, which is considered genius-level, with rumors among her classmates placing her IQ at around 300. She consistently achieves the highest scores on national exams and has a particular aptitude for mathematics and science. However, this academic prowess has ironically been the source of her loneliness. Her peers often mistake her quiet and reserved demeanor for snobbery or arrogance, leading them to believe she thinks she is too good for them. Consequently, before the events of the series, Ami had few, if any, friends and spent most of her time studying in solitude, feeling alienated and isolated. In Crystal, her initial shyness is pronounced, but she possesses a fundamentally kind, gentle, and polite personality. She is well-mannered and dislikes conflict and any action that would cause harm to innocent people.

Ami's motivation and life change dramatically when she meets Usagi Tsukino. Usagi, who is her academic opposite, persistently seeks Ami's help with studying and, more importantly, sees past her intimidating intellect to the lonely girl beneath. Usagi's genuine and unreserved friendliness breaks through Ami's isolation, and she quickly comes to value this new connection above all else. This loyalty is a core part of her character. When she is brainwashed by the Dark Kingdom at a cram school called the Crystal Seminar, it is the sight of Sailor Moon in danger that awakens her latent powers. With the guidance of the feline advisor Luna, she receives her transformation pen and awakens as Sailor Mercury, the Guardian of Water and Wisdom.

Within the group of Sailor Guardians, Ami's primary role is that of the strategist and analyst. She is the brains of the operation, providing a calm and level-headed perspective that often tempers the more impulsive actions of her friends. Her ability to quickly analyze an enemy's weaknesses and the surrounding environment is invaluable in battle. She is frequently the voice of reason, and her unwavering loyalty is to Sailor Moon, the team's leader and her beloved princess, for whom she is willing to sacrifice her life.

Her key relationships are forged through her shared duty as a Guardian. Her friendship with Usagi is the most transformative, as it is the first true friendship she has ever had. Through Usagi, she meets and forms strong bonds with the other Inner Guardians: Rei Hino (Sailor Mars), Makoto Kino (Sailor Jupiter), and Minako Aino (Sailor Venus). The series also establishes a significant connection to the past. During the age of the Silver Millennium, Ami's past life was Princess Mercury, who dwelt in Mariner Castle. In the Crystal continuity, it is clearly established that she and Zoisite, one of the Four Kings of the Dark Kingdom, were in love during that previous era, adding a layer of tragic history to her present-day battles.

Throughout the series, Ami undergoes notable development. She transitions from a painfully shy, isolated bookworm to a confident and integral member of a tight-knit team. While she remains studious and serious, she learns to embrace friendship, fun, and her role as a protector. Her unwavering loyalty is tested when she is given the opportunity to study abroad in Germany to pursue her medical dreams, a path that would separate her from her fellow Guardians. Ultimately, she chooses to remain with her friends, having found a purpose and a family that she is not willing to abandon. This decision shows her growth from a girl who craved approval and academic success to one who values love, friendship, and her mission as a Sailor Guardian above all else.

As Sailor Mercury, Ami possesses abilities related to water, ice, and intelligence. Her signature ability is to generate a mist or fog, which she uses to obscure the enemy's vision and analyze their movements. She is also equipped with a visor and a small supercomputer that allow her to scan for enemy weak points, track life forms, and devise battle plans in real time. Her primary offensive attacks involve projecting powerful streams of water that can freeze upon contact, trapping her opponents in ice. As she gains more experience and her powers grow stronger, her abilities become more sophisticated, allowing her to perform even more powerful hydrokinetic and cryokinetic feats.