Nasa Yuzaki received his name from parents who chose kanji for "starry sky," dreaming he'd embody space's vastness. Childhood mockery over sharing the name with NASA fueled his intense academic drive to transcend ridicule. He consecutively topped national middle school exams but forfeited formal education after a life-changing accident disrupted entrance exams. While crossing a snowy street during high school planning, he spotted Tsukasa Tsukuyomi and stepped into traffic, mesmerized. An oncoming truck struck him, though Tsukasa absorbed part of the impact. Despite severe injuries, he chased her to a bus stop, likened her to the moon princess Kaguya-hime, and confessed. She agreed to date only if they married, and he instantly consented before collapsing. Hospitalized without learning her name, he worked delivery jobs alone for years, awaiting reunion. On his eighteenth birthday, she arrived at his apartment with marriage documents, honoring their pact. Post-marriage, Nasa balances logical prowess with social awkwardness. He calculates nutritional meals yet defaults to daily hot pot, insures belongings compulsively—proven wise when their apartment fire caused minimal loss—and masters programming, engineering, and accounting to rescue the Arisugawa bathhouse financially while mentoring the owner's daughter. Pop culture gaps leave him dependent on Tsukasa. He voices unfiltered devotion through loud public declarations, embarrasses her with jealousy over past male acquaintances, and bristles when others see her in revealing attire. Privately, he seeks physical closeness, savoring her scent and intimate moments. He evolves toward bolder romance without shedding core traits: gifting Tsukasa a smartphone to ease separation anxiety, prioritizing understanding over anger during her absences, and accepting her immortal heritage by focusing on support. Initially oblivious to classmate Aya Arisugawa's feelings, he later acknowledges them respectfully. Safety remains paramount—his first reaction to their burning apartment was checking for casualties.