Kei Yuki hails from a timeline roughly one thousand years beyond Siren's Port. Rescued by Captain Harlock during a raid on a prison transport, she joined the Arcadia crew after her arrest for assaulting a military officer who disparaged her father's death. With her parents deceased and her fiancé, Kazuya Katagiri, vanished, she dedicated herself to the starship and its captain. Her Earth-bound past centered on her father's research into long-term space colonization, cut short when a laboratory accident claimed his life; her mother later succumbed to grief. Kazuya eventually reappeared, ostensibly continuing her father's work, but was exposed as a collaborator with the alien Mazone race and responsible for the fatal accident. Kei confronted and shot him before returning permanently to the Arcadia. Serving as the Arcadia's chief navigator and science officer, Kei operated detection systems and analyzed scientific data, recognizable in her distinctive pink suit and maintaining a professional demeanor amidst the crew's eccentricities. Her relationships varied across continuities: initial romantic interest in Tadashi Daiba shifted to platonic friendship, while later iterations like "Endless Orbit SSX" depicted unrequited feelings toward Captain Harlock. The 2013 film adaptation showcased her combat skills as an Action Girl and ship tease with crewmates Logan/Yama and Yullian. After the Mazone conflict, continuity paths diverged. Some narratives placed her building an observatory on Earth with Tadashi Daiba, others depicted her commanding her own ship, the Fluorite, years after the Arcadia's disbandment. In this latter scenario, Earth authorities captured her and sentenced her to execution, only for Harlock to rescue her, facilitating her return to the crew. During the battle against the demonic Noo entities, Kei entered a coma after taking a bullet for Tadashi Daiba. Her body was possessed by a Noo spirit while her soul wandered in limbo, uncovering Noo secrets before Daiba's intervention restored her. Transported to Siren's Port following the Arcadia's final implied missions, Kei adapted to urban life by performing odd jobs under aliases like Mayu Oyama. She worked at Icha Icha Paradise under Hatake Kakashi while secretly investigating environmental hazards around Whithers Lake and organizations like AGI and SERO using her touchpad NV device's scientific analysis capabilities. SERO agent encounters prompted her to cut her hair and use wigs for disguise. An earthquake during a lake investigation caused a leg wound and minor radiation poisoning. After an attack destroyed Icha Icha Paradise and Kakashi disappeared, she relied on stored finances while investigating his absence. Personality-wise, Kei balanced positivity and professionalism, often acting as a stabilizing influence. Betrayal by Kazuya fostered emotional guardedness, yet fierce loyalty to allies persisted. Living among the Arcadia's crew cultivated a flirty sense of humor, though she rejected criticism about her appearance or weight. In Siren's Port, she displayed maternal tendencies toward vulnerable individuals while struggling with confinement-induced stress, adhering to the Arcadia's motto of freedom under adversity. Her acquired ability, Acute Navigation, granted perfect recall of routes to previously visited locations. Close connections in Siren's Port included Edgeworth, Zexion, Sam Merlotte, Riku, Kakashi, and Ellis. She contributed environmental data to Loyaltous's faction-neutral network, maintaining her role as a pragmatic investigator despite unemployment after SERO's attack on her workplace.