Tsukasa Yuzaki, originally named Tsukasa Tsukuyomi, originates from ancient Japanese folklore as the daughter of a servant assigned to destroy the Elixir of Immortality from the Tale of the Bamboo Cutter. Her father administered the elixir to save her from critical illness, granting her immortality. She has lived over 1,400 years without aging, retaining the physical appearance of a 16-year-old girl. Her extensive lifespan provides firsthand historical knowledge, enabling her to recount events as though she witnessed them. She speaks archaic languages, practices traditional customs like wearing yukata, and wields historical weapons such as katanas with proficiency. She observes historical shifts in landscapes and infrastructure, contrasting past travel hardships with modern conveniences like buses. Immortality grants her supernatural traits: rapid regeneration from fatal injuries like severed limbs or aerial bombardments, disease resistance, and healing blood. Her durability allows survival from impacts that would kill ordinary humans, evidenced when shielding Nasa Yuzaki from a truck collision. Despite these abilities, her adolescent physique leaves her vulnerable to superior physical force. Initially calm and emotionally reserved during her first meeting with Nasa, she gradually reveals deeper emotions after marriage, frequently flustering at his affectionate declarations and showing jealousy over his interactions with others. She demonstrates kindness by prioritizing Nasa's well-being, tending to his injuries, and managing household finances frugally. Her interests passionately embrace modern pop culture, movies, and video games, contrasting her ancient origins. Her relationship with Nasa defines her development. She saved him from a traffic accident on a snowy night, immediately accepting his marriage proposal. After vanishing for two years, she reappeared with marriage documents to formalize their union. As spouses, they navigate daily challenges like budgeting and conflicts, with Tsukasa often proposing practical solutions. She increasingly expresses vulnerability and affection but initially conceals secrets about her past. She shares a complex bond with Chitose Kaginoji, whom she considers a sister despite Chitose's early disapproval of her marriage. She maintains a respectful relationship with Kaname Arisugawa. The "Bride Gallery" project chronicles her pre-Nasa struggles across historical eras through monthly illustrations. Lunar motifs recur in her life, emphasized by her ownership of an Apollo mission moon rock gifted by her grand-aunt Tokiko. This connection, paired with Nasa's space-themed name, symbolizes their intertwined fates. Her narrative explores enduring centuries of loneliness and seeking normalcy through human bonds.