Michiru Kaiō, whose name translates as "Rising Sea King," is the civilian identity of Sailor Neptune, Guardian of Deep Waters. This role reflects her association with Neptune, the Roman god of the sea. She possesses deep blue eyes and wavy teal hair, maintaining an elegant and sophisticated appearance. Her civilian demeanor is graceful and artistic; she excels as a violinist and painter. Michiru attends Mugen Academy alongside her partner, Haruka Tenō, displaying high intelligence and refined tastes. Sailor Neptune derives her powers from the Neptune Crystal, centering on oceanic manipulation. She generates tsunamis, controls seawater, and wields precognitive abilities, often sensing disturbances through phrases like "the sea is stormy." Her primary weapon is the Deep Aqua Mirror, a Talisman revealing hidden truths, dispelling illusions, and enabling astral projection. Secondary weapons include the Marine Cathédrale violin, used in the attack Submarine Violon Tide to unleash hypersonic waves. Her transformation phrases evolve from "Neptune Planet Power, Make Up!" to "Neptune Crystal Power, Make Up!" after obtaining her Sailor Crystal. Key attacks include Deep Submerge, an energy blast, and Submarine Reflection, a mirror-based assault. Michiru balances elegance with pragmatic ruthlessness. She prioritizes her Guardian duty over personal attachments, agreeing to sacrifice Hotaru Tomoe to prevent Sailor Saturn's destructive awakening. She shares a romantic relationship with Haruka Tenō, emphasizing mutual devotion; they vow to kill each other if possessing a Talisman endangers their mission. Despite her calm exterior, she exhibits fierce loyalty, declaring a world without Haruka "isn't worth living in." In Sailor Moon Crystal Season III, she infiltrates Mugen Academy to monitor the Death Busters. Her Deep Aqua Mirror resonates with the Holy Grail, enabling Sailor Moon's Super transformation. During the final battle against Pharaoh 90, she erects a protective barrier over Mugen Academy but falls when it shatters. Supplemental materials depict her past life as Princess Neptune of Triton Castle. Following the Infinity arc, she resides with Haruka, Setsuna Meiō, and the reincarnated Hotaru, forming a familial unit.