Natsu Iwashimizu's final memory of her family involves sharing her favorite meals with them. Tragically, she awakens from this dream to discover she is on a sinking ship, being rescued by three strangers: Arashi Aota, whose kind nature clashes with his quick temper; Semimaru Asai, who takes pleasure in mocking Natsu's timid demeanor; and Botan Saotome, a capable woman who appears to understand their predicament. After the group of four successfully escapes, they sail toward a deserted island. Unbeknownst to them, this mysterious island is Japan. Following a meteorite impact on Earth, humanity was eradicated and the environment underwent drastic changes. To repopulate the nation, the government launched the "7 Seeds" project, comprising five groups—Spring, Summer A, Summer B, Autumn, and Winter—each consisting of seven healthy young individuals and a guide. Natsu and her companions were assigned to team Summer B, whose members are viewed as failures by society. To secure additional supplies, the group must locate one of the seven shelters constructed by the government. In a hostile, unfamiliar world devoid of loved ones to rely on, the quartet must learn to cooperate with one another to ensure their survival.