Tsukasa Tsukuyomi, later adopting the surname Yuzaki upon marriage, carries a history stretching back 1,400 years. Her immortality began when her father, Yakusa, defied the emperor's decree and administered the forbidden Elixir of Hourai to cure her terminal illness. This act saved her life, eternally preserving her at sixteen, but brought severe punishment upon her family. Her existence is interwoven with the events surrounding the Japanese legend of Princess Kaguya, though she is not Kaguya herself. Centuries of life allowed her to witness and participate in pivotal historical moments across continents. She interacted with significant figures: Prince Shotoku, who named her "Tsukasa" expressing a wish for her to "govern human history"; Oda Nobunaga; Tokugawa Yoshimune; and former U.S. President Dwight D. Eisenhower, whom she called "Ike." These experiences granted her vast historical knowledge, proficiency in traditional combat like katana handling, and the ability to read ancient texts, though modern technology often confuses her. Physically, she appears as a petite girl standing 154 cm tall, with long pink hair and red eyes. Her typical attire includes an elegant white long-sleeve shirt, mini black skirt, and pink socks. At home, she prefers modern sleepwear: a long-sleeved pink shirt and striped pajama pants. She constantly wears a cherished deer leather barrette, a centuries-old gift from an emperor. Initially presenting as cool and emotionally reserved, her personality unfolds after marrying Nasa Yuzaki. She frequently displays embarrassment over romantic gestures, jealousy when Nasa compliments other girls, and competitiveness when challenged. Her kindness manifests through domestic care, cooking elaborate meals and managing household finances prudently. She harbors a passionate enthusiasm for pop culture—films, video games, and anime—often expressing childlike excitement over technology like televisions or retro game consoles. Her narrative arc pivots when she saves Nasa from a truck accident on a snowy night. After his confession, she agrees to become his girlfriend only if he marries her. Disappearing for nearly two years, she later arrives at his doorstep with marriage paperwork, initiating their union. As their relationship develops, she adopts his surname and navigates everyday marital experiences, including cohabitation logistics, shared nicknames ("Tsukasa-chan"), and hand-holding. Her immortality creates underlying tension, particularly with her adoptive sister Chitose Kaginoji, who initially opposes the marriage. Following the burning of their first apartment, Tsukasa works part-time at the Arisugawa bathhouse, forming bonds with coworkers Kaname and Aya Arisugawa. Despite supernatural resilience—immunity to illness and the strength to overpower wild animals—she strives for normalcy, cherishing mundane moments with Nasa and longing to overcome her eternal solitude through their bond. Minor traits include her proficiency in sushi-making, restless sleeping habits, love for memory foam futons, and spontaneous enjoyment of nighttime adventures. She occasionally references historical anecdotes as personal memories but avoids elaboration, maintaining an air of mystery about her past.