Neptune and her friends arrive at "My Summer Vacation Mountain," a place overflowing with lush greenery, to enjoy their vacation. The four goddesses of the four nations are together again after a long time, and they engage in their usual lively banter. Meanwhile, Nepgear sets out for a walk in the mountains with her sisters, Uni and the others. Along the way, the sisters pass through a long row of large torii gates and find themselves lost in another dimension...