Along with three others, Natsu wakes up with no idea what's happened. The four of them reach an island and 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. Finally, Botan reveals what she knows.
Natsu's clumsiness indirectly leads Team Summer B to the rest of their group. Her memories help them figure out their location, and their next moves.
Arashi, Natsu and Semimaru stumble upon 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 the sole survivor of Team Winter. Team Spring reaches Mt. Ogino Fuji and finds Natsu's message.
Aramaki joins Team Spring, despite Fujiko's 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 those who took refuge there.
Hana's group and the Team Autumn survivors find the Spring settlement destroyed and abandoned. Momotaro wakes up among strangers.
To survive, Hana and the others work together with Team Summer A. On the ship, Hotaru's cousin Hibari 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 Team Summer A members.
Hana becomes convinced that Ango will kill her if she stays in the village. Natsu and the others make landfall near the former Autumn settlement.
Ryo orders Hana to join him in searching for a water source underground, putting her in a vulnerable position. In the caves, Ango recalls Shigeru.
Team Summer A banishes Ango and Ryo as Haru and the others mourn the missing Hana. Aramaki leaves the settlement believing she is still alive.
Expecting a trap, Ango and Ryo find and observe Team Summer B, but they are unexpectedly welcomed by the easygoing group.
The two newcomers help Team Summer B. As they get to know the group, Ryo doubts their ability to survive. Ango begins to see Natsu as Shigeru.
The carefree group enjoys life at sea, but Ryo tests their survival skills. Natsu reveals that Team Summer B is for dropouts, angering Ango.
Suspicious, Botan searches Ryo and Ango's belongings while the others look for Arashi. Elsewhere, another survivor learns about the wilderness.
Team Summer B gets stuck in a bed of dense algae. They find a large ship and investigate, but Botan is wary. Stranded, Arashi sees the ship's kite.
The team members are separated after the ship's sudden movement. Arashi makes his way to help as Botan's group makes a discovery.
Ango's hallucinations lead to perilous situations for him and Arashi. Semimaru has a brush with death while Natsu gathers her courage.
A sanctuary in nature becomes a trap for small mammals and humans alike. Meanwhile, an iron-eating bacteria begins to spread throughout the ship.
Fujiko and Chisa reunite with Hana. On the ship, the missiles begin launch prep while Team Summer B learns about Ango's past and the test.
Hana readjusts to other humans. Team Summer B works together to manually disable the missiles, but a series of passcodes complicates the process.
Problems persist in the ship as the spreading bacteria begins attacking. The missile countdown continues as the team makes a mad dash to exit.