Tsukasa Yuzaki, originally called Tsukuyomi, serves as the central female character. Born over 1,400 years ago during the Asuka period, she consumed the elixir of immortality to cure a fatal disease. Her father, Yakusa, defied Emperor Tenji by giving her the elixir instead of destroying it, leading to her family's punishment while she survived eternally. Across centuries, she witnessed pivotal historical moments and encountered figures such as Prince Shotoku (who bestowed the name "Tsukasa," meaning "to govern human history"), Oda Nobunaga, and Tokugawa Yoshimune. Despite her vast age, she retains the physical form of a 16-year-old girl. Physically, Tsukasa possesses long pink hair, red-pink eyes, and stands 154 cm tall. She favors elegant attire, often seen in a white long-sleeve shirt, black mini skirt, and pink socks. At home, she prefers modern sleepwear like a pink shirt or striped pajamas. Her petite frame belies supernatural capabilities: immense strength, agility, and combat mastery enable her to defeat bears or wolves barehanded and wield katanas expertly. She exhibits mid-level regeneration, recovering from fatal wounds like aerial bombardments or severed limbs, and remains immune to aging and illness. Conversely, modern technology like smartphones and remote controls often confounds her. Personality-wise, Tsukasa initially appears calm, level-headed, and mysterious, but gradually reveals deeper facets. She embarrasses easily, particularly regarding romantic affection, and shows occasional jealousy. Inherently kind, she cares deeply for others, especially her husband, Nasa Yuzaki. Her interests encompass a passion for pop culture—movies, anime, retro games—and simple pleasures like late-night adventures or comfortable futons. She is competitive, readily accepting dares, though she moves excessively while asleep. Her relationship with Nasa drives much of her development. She first encountered him on a snowy night, saving him from a truck accident. After Nasa confessed his love, she agreed to be his girlfriend only if he married her first. Disappearing for nearly two years, she returned on Nasa's 18th birthday with marriage paperwork, initiating their life together. Adopting his surname to become Tsukasa Yuzaki, she encourages affectionate nicknames ("Tsukasa-chan" from Nasa; she calls him "Nasa-kun"). Her love manifests practically: she excels at cooking diverse meals, manages household finances frugally, and works part-time at the Arisugawa bathhouse after their first apartment burned down. She treasures their shared life, expressing sentiments like feeling "proud" in a large home or "warmth" in a small one. Various OVAs and seasons further explore Tsukasa. The "SNS" OVA sees her navigating social media with Nasa. The "Uniform" OVA features her wearing a school uniform on a date. Season 2 delves into her immortality and historical connections, deepening her emotional bond with Nasa as she confronts her past solitude. The "High School Days" OVA arc depicts her attending school alongside Nasa. Throughout all media, her character arc focuses on embracing vulnerability and human connection after lifetimes of isolation, evolving from a detached figure into a devoted partner who cherishes everyday moments with Nasa.