Shidou Itsuka meets the strange Kurumi Tokisaki on the day of the Tanabata celebration, who continues to ask him out on a date. Shidou accepts the proposition despite his reservations. The two spend their day touring a planetarium, shopping at a festival, and practicing a pretend wedding ceremony. Meanwhile, Shirou's pals, Takea Yatogami, Yoshino, and Kotori Itsuka, are searching for him while also enjoying the festival. Shidou notices an unexpected gentler side of Kurumi as he spends the day with her. He is aware that Kurumi is popularly known as the "Worst Spirit," yet the girl in front of him is a compassionate spirit. However, as the day comes to a close, Shirou begins to see the reality behind it all.