Michiru Kaiō is the civilian identity of Sailor Neptune, a member of the Outer Solar System Sailor Guardians who first appears in the third season of Pretty Guardian Sailor Moon Crystal, known as the Death Busters arc. She is a talented and internationally recognized violinist who also excels in painting and swimming. Raised in an affluent environment, she carries herself with an elegant and sophisticated demeanor, often speaking in a polite and refined manner. Beneath her composed exterior lies a deeply passionate and occasionally fierce personality, capable of sharp anger when provoked. She is fully dedicated to her duty as a Sailor Guardian, which she approaches with a sense of solemn responsibility. Unlike the Inner Guardians who protect Earth and its princess, Michiru and her partner Haruka Tenō, Sailor Uranus, operate from the outer solar system, tasked with defending the entire solar system from external threats. This broader mission often forces them to make difficult choices, including sacrificing individuals for the greater good, a burden they carry with gravity. Her strongest bond is with Haruka Tenō, with whom she shares a romantic and deeply committed partnership. The two live together and operate as a seamless team in battle, often strategizing privately and acting without consulting the other Guardians. They initially view the Inner Guardians as naive and distrust their approach, preferring to handle threats on their own. Over the course of the season, Michiru develops a cautious respect for Usagi Tsukino, Sailor Moon, and eventually recognizes her as a true leader. Her primary artifact is the Deep Aqua Mirror, a talisman that grants her the ability to see into the future and perceive hidden truths. As Sailor Neptune, she commands the power of the deep seas and oceans, unleashing attacks such as Deep Submerge. She is associated with the planet Neptune and embodies the qualities of deep water: calm and serene on the surface, but possessing immense depth and hidden strength. Her motivations are rooted in a profound sense of duty inherited from her past life during the Silver Millennium, where she and the other Outer Guardians patrolled the boundaries of the solar system. In Crystal Season III, she is first encountered as a student at the Infinity Academy, where she and Haruka investigate the Death Busters, a group of parasitic aliens. Throughout the season, she grapples with the ethical implications of her mission, particularly when it comes to the potential awakening of Sailor Saturn, a guardian whose power could destroy the world. Her loyalty to Haruka remains unwavering, and her development sees her moving from a position of moral absolutism toward a more nuanced understanding of protection and sacrifice. By the season's end, she acknowledges Sailor Moon as the true messiah and entrusts the future to her, allowing herself to step back from the front lines.