Along with three others, Natsu wakes up without an idea of what has happened; the quartet reaches an island to try to figure out a way to survive.
Convinced that Botan has kidnapped them, Natsu and Arashi sneak out of camp and run into another survivor; Botan reveals what she knows.
Natsu's clumsiness indirectly leads Team Summer B to the rest of the group; her memories help them figure out their location -- and their next moves.
Arashi, Natsu and Semimaru stumble on the Team Autumn settlement in the former Kobe region; they seem to be thriving, but their leaders are tyrants.
In the ruins of Tokyo, Natsu, Arashi and Semimaru meet Team Winter's sole survivor; Team Spring reaches Mount Ogino Fuji and finds Natsu's message.
Aramaki joins Team Spring, despite Fujiko having doubts; Hana decides to search for Arashi after hearing that Aramaki met someone who fits his description.
Hana and her companions discover a massive underground shelter; they find a survivor's diary and learn the cruel fate of the people who took refuge there.
Hana's group and the Team Autumn survivors find the Spring settlement destroyed and abandoned; Momotaro wakes up among a group of strangers.
To survive, Hana and the others work together with Team Summer A; on the ship, Hibari, Hotaru's cousin, tells Natsu that Hotaru is slowly dying.
Ango recalls his harsh upbringing in the program and the brutal graduation test that winnowed the survivors down to the final members of Team Summer A.
Hana becomes convinced that Ango will kill her if she stays in the village; Natsu and the others make landfall close to the former Autumn settlement.
Ryo orders Hana to join him in searching for a water source underground, which puts her in a vulnerable position; in the caves, Ango recalls Shigeru.