In the year 200X, an explosion with an unknown cause occurs during a flight test of a supersonic business jet off the coast of Shikoku. A month later, a similar accident occurs during a flight test of the Japan Air Self-Defense Force heading from Gifu to Shikoku. Meanwhile, in Kochi, near the site of the plane crash, a boy named Shun is walking on the beach. His father is an Air Self-Defense Force member who was on board the crashed aircraft, and he finds a mysterious, squishy object on the beach...

(Source: Natalie, translated)