Hotaru Tomoe, daughter of scientists Souichi and Keiko Tomoe, suffered severe injuries and lost her mother in a childhood lab accident. To save her, Souichi performed experimental cybernetic modifications, replacing damaged limbs while unknowingly implanting a parasitic Daimon egg from the Tau Star System. This egg developed into Mistress 9, causing Hotaru chronic seizures and physical frailty, leading to ostracization. She concealed her cybernetic body under long sleeves and dark clothing, living isolated until befriended by Chibiusa, who showed no fear of her condition or latent abilities. Mistress 9 gradually assumed control, using Hotaru as a vessel to steal Chibiusa's Silver Crystal and summon Pharaoh 90. During possession, Hotaru's consciousness resisted internally, protecting Chibiusa's spirit. When Sailor Moon appeared defeated, Hotaru awakened fully as Sailor Saturn, Guardian of Silence and Destruction. Wielding the Silence Glaive, she destroyed Pharaoh 90 and the Death Busters' dimension at the cost of her life, triggering planetary rebirth. Sailor Moon resurrected Hotaru as an infant, free of cybernetics and Mistress 9. With Souichi deceased, the Outer Guardians—Haruka Tenoh (Sailor Uranus), Michiru Kaioh (Sailor Neptune), and Setsuna Meioh (Sailor Pluto)—adopted her, raising her in their Victorian-era home. Reborn Hotaru initially lacked past memories. She rapidly aged from infancy to a physically small child, displaying exceptional intelligence and a cheerful demeanor, though occasionally exhibiting detached mannerisms reminiscent of Sailor Saturn. She cherished reading, formed a close bond with Chibiusa, and attended school with her. This peace was interrupted by the Dead Moon Circus invasion. Sailor Saturn's spirit communed with Hotaru, restoring her memories and catalyzing a second rapid aging to early adolescence. Hotaru then formally reawakened as Super Sailor Saturn, unifying her human identity and Sailor Guardian consciousness. In *Sailor Moon Eternal*, Super Sailor Saturn played a pivotal role against the Dead Moon Circus. She bestowed the Sailor Crystals upon Haruka, Michiru, and Setsuna, enabling their transformations into Super Sailors Uranus, Neptune, and Pluto. Alongside Sailor Chibi Moon, she confronted the corrupted Amazoness Quartet within the circus tent, identifying them as brainwashed Sailor Guardians. After Zirconia trapped both in glass shards, Sailor Moon freed them. Sailor Saturn safeguarded the Quartet's containment orbs, enabling their eventual purification and revelation as the future Sailor Asteroid Guardians—Ceres, Pallas, Juno, and Vesta. Sailor Saturn's powers center on annihilation and renewal. Her Silence Glaive can eradicate planets or star systems, facilitating cosmic rebirth. She also projects defensive barriers (Silence Wall), heals minor injuries, detects magic, and creates illusions. After reawakening, she gained the Saturn Crystal, evolving into Super Sailor Saturn with enhanced abilities. Later, she attained the Eternal form, mirroring Eternal Sailor Moon's power level. In the Silver Millennium, she existed as Princess Saturn, residing in Titan Castle, dormant until the kingdom's fall. Her title "Guardian of Ruin and Rebirth" reflects her necessary cosmic role. Her name carries symbolic weight: "Hotaru" (蛍, firefly) references spirits of the dead in Japanese mythology, aligning with her association to destruction and rebirth. "Tomoe" (土萠) combines "earth" (土) and "sprouting" (萠), with the first kanji matching the Japanese name for Saturn ("Dosei" - 土星). Together, her name signifies "firefly sprouting from Earth."