Second season of Katainaka no Ossan, Kensei ni Naru.

Twenty thousand years after the fall of humanity, Earth succumbed to legions of ravenous creatures who now freely roam the planet. Far away in the depths of space, the last surviving members of humanity float aimlessly in the same ship they escaped Earth with so many years ago. With the spacecraft running dangerously low on resources, the survivors' leading council must decide on their path forward: should they continue to gamble on finding another Earth-like planet to inhabit, or take to heart an anonymous essay theorizing what may be the only weakness of the Godzilla, who forced the last remnants of humanity off their home world? The author of the controversial essay is Haruo Sakaki, a man who witnessed the death of his parents to Godzilla at a young age, which has led him to harbor an obsessive hatred for the monster. Now, he spearheads the operation aimed at reclaiming humanity's birthright from the king of monsters and slaying him once and for all. But, alongside humanity, Earth has undergone drastic change since their departure; Godzilla and its numerous spawns may pale in comparison to the darkness lurking within the hearts of this close-knit community of survivors.

In a dark void known as the Lightless Realm, a group of children meet and bond, but are then separated and returned to their own dimension. Years later, these children reunite to fight Admonitions, monsters that originate from the same void, using robots known as Vess. However, their efforts only slow the ever-encroaching and expanding Lightless Realm from infecting their world. Their lives take a drastic turn when a new foe appears in the form of a Corpse, whose song is rumored to kill any who hear it within nine days. The Corpse Song is heard by the group, and with this, they each begin to pull away and become caught up in their own personal problems—ultimately threatening the fate of humanity.

After getting permission to show their film at the cultural festival, the Pastime Club fervently discusses what they plan to wear for the big event. The conversation soon takes to the next level, and the three girls begin to put their costume ideas to the test. The Film Studies Club decides to write letters to their future selves in 15 years on the Macintosh computer donated by Chisato Higuchi's father. Despite setting ambitious goals and promises, reality turns out different than they expected.