Setsuna Meiō, Guardian of the Door of Space and Time under Queen Serenity’s mandate, enforces three sacred taboos: protecting the dimensional gateway, forbidding unauthorized time travel, and never halting time’s flow—each violation punishable by fatal consequences. Isolated for millennia outside linear existence, she inherits Chronos’s divine lineage, wielding authority over spacetime and detecting temporal disruptions. During the Black Moon conflict, her loyalty fractures when she freezes time to avert a cataclysmic clash between past and future Silver Crystals, defying her third taboo to sacrifice herself. Neo-Queen Serenity resurrects her as a mortal, Setsuna Meiō—a physics student navigating human life while retaining her Senshi duties, granting her first taste of ordinary existence. Allying with Sailor Uranus and Neptune in the Death Busters arc, she confronts existential threats like Pharaoh 90, forming a protective triad with Hotaru Tomoe, Sailor Saturn’s host. Their bond deepens into a familial unit, sheltering Hotaru’s reborn form. Setsuna also guides Ami Mizuno (Sailor Mercury), fostering their intellectual synergy to unlock Ami’s Super transformation. Her arsenal spans spatial rifts, teleportation, and spacetime barriers conjured through the Garnet Rod and Orb. Combat techniques like Dead Scream and Chronos Typhoon underscore her tactical precision, while the Time-Space Key permits regulated temporal navigation. Evolved as Eternal Sailor Pluto, her upgraded attire mirrors heightened cosmic stewardship. Though reserved, she nurtures a tender mentorship with Chibiusa, pivotal in purging the child’s Black Lady corruption. Later chronicles—Dream, Stars, and the Eternal/Cosmos films—depict her dual existence: vigilant spacetime sentinel and Princess Pluto, guardian of the Pluto Crystal across realities. Subtle musical adaptations imply latent affection for King Endymion, though canon prioritizes her unwavering duty. Reborn into humanity, she embraces mundane joys—fashion design, shopping—and bridges celestial obligation with mortal bonds, her arc epitomizing sacrifice and rebirth’s redemptive grace.