Nasa Yuzaki is a brilliant but socially awkward young man who has his life mapped out until a fateful encounter on a snowy night changes everything. After being struck by a truck, he is saved by a mysterious and beautiful girl named Tsukasa. Smitten, Nasa confesses his feelings, and Tsukasa agrees to date him only if they get married first. She disappears shortly after, only to reappear years later at his doorstep with a marriage registration form, officially beginning their life together as husband and wife. The series follows the newlyweds as they navigate the complexities of living together, building intimacy, and learning about each other's quirks. While the premise is rooted in a sudden marriage, the show focuses on the wholesome, comedic, and heartwarming development of their relationship. As they settle into their domestic life, the mystery surrounding Tsukasa's past and her seemingly ageless nature begins to hint at a deeper, more supernatural connection that transcends ordinary romance.