Michiru Kaioh, internationally renowned as both a teenage violinist and artist, exhibits exceptional talent and maturity. Her surname translates to "Sea King," reflecting oceanic associations, while her given name means "rising," resulting in the full meaning "Rising Sea King." She possesses deep blue eyes and wavy teal hair falling just past her shoulders, maintaining an elegant, refined appearance through sophisticated fashion and meticulous grooming. Her grace and femininity often evoke the perception of a fairy-tale princess, carrying an aura of quiet sophistication. She attended Mugen Academy, a prestigious institution for genius-level students, where she infiltrated to investigate the Death Busters organization alongside her partner, Haruka Tenoh. Wealthy and independent, Michiru owns personal assets like the manga-depicted helicopter Kaio Maru. No known relatives are documented across media; following the Infinity arc, she forms an adopted family unit with Haruka, Setsuna Meioh, and Hotaru Tomoe. Personality-wise, Michiru exhibits calmness, patience, and acute perceptiveness, often masking her true thoughts. She displays kindness "as great as the sea" but dislikes patronization, revealing sharp anger or a temperamental side when provoked. Her dedication to Sailor Guardian duties is absolute, prioritizing mission success over individual lives, including her own—a stance contrasting with the Inner Guardians' more compassionate approach and occasionally causing friction. Her artistic passions extend beyond violin to painting, with works exhibited in galleries, and she excels in swimming. Personal preferences include a favorite color of marine blue, sashimi as her preferred food, and a dislike of kikurage mushrooms and sea cucumbers. Her closest bond is the explicitly romantic relationship with Haruka Tenoh (Sailor Uranus), confirmed across manga, anime, and musicals. The pair operate as inseparable partners, described as complementary opposites—Michiru embodying a feminine, artistic presence while Haruka carries a more masculine energy. Their relationship withstands extreme tests, including mutual willingness to sacrifice the other if compromised during missions. In the Sailor Stars arc, they temporarily align with Sailor Galaxia under false pretenses to steal her star seed, accepting potential eternal damnation as long as they remain together. Their final act before dissolution involves reaching for each other's hands, symbolizing unwavering commitment. As Sailor Neptune, she protects the solar system's outer edges from external threats, wielding powers tied to Neptune's oceanic mythology. These include commanding and shaping seawater, precognition (often signaled by stating "the sea is stormy"), and astral projection. She channels these powers through her Talisman, the Deep Aqua Mirror, which reveals hidden truths, dispels illusions, and weakens enemies. Her violin, the Marine Cathédrale, serves as a manga weapon enabling the Submarine Violon Tide attack. Her transformation phrases evolve from "Neptune Planet Power, Make Up!" to invoking "Neptune Crystal Power" upon obtaining her Sailor Crystal, the source of her abilities. Her Sailor Guardian form features a teal-and-cerulean uniform with a dark green gem-adorned choker and deep teal skirt. Evolved forms include Super Sailor Neptune, marked by a lengthened back bow, heart-shaped front bow, and translucent shoulder pads. Eternal Sailor Neptune introduces star motifs, a V-shaped choker, light sea-green bubble sleeves, knee-length boots, and extended ribbons. Her Silver Millennium incarnation as Princess Neptune wears a sea-green gown, residing in Triton Castle. Character development shows initial reluctance to collaborate with the Inner Guardians due to conflicting methodologies, particularly regarding Hotaru Tomoe's potential as Sailor Saturn. This stance softens after witnessing Sailor Moon's resolve, leading to pledged loyalty. Her narrative arc includes significant sacrifices, enduring temporary death alongside Haruka during battles against the Death Busters and later against Galaxia, culminating in resurrection and continued guardianship aligned with the Sailor Guardians' unified cause.