Hikaru Kohinata, who grew up in the small town of Izu, and Futaba Ohki, who moved from Tokyo. The two who entered Yumegaoka High School together found a lot of happiness in rebreather diving and ordinary daily events. Futaba, who used to be very negative about everything, experienced a lot of joy of taking a step forward under the influence of Hikaru, who is always cheerful and optimistic. Not only that, Futaba also passed the long-awaited open water diver internship, and will aim to become an advanced open water diver next. This one-time, irreplaceable high school life is just about to begin. The wonderful days are not over yet, and the days they have spent together will continue.