With summer vacation coming to an end, the girls are making the most of their remaining time. Their everyday antics are cut short, however, when Suguru Koshigaya wins the top prize of a lottery—tickets to Okinawa! Following hurried preparations, the Asahigaoka gang departs on a three-day journey for their final summer vacation. When the gang arrives in Okinawa and checks into an inn, they meet Aoi Niizato, the young daughter of the inn's hostess. Despite their comparable ages, Natsumi Koshigaya is struck by her mature manner, which causes her to reflect on her own childlike character. With the blossoming of an unexpected relationship on the horizon, the girls waste no time in launching into their ambitious sightseeing plans and regional activities!