In a world plagued by creatures known as Kaiju, Kafka Hibino aspired to enlist in The Defense Force. He makes a promise to enlist with his childhood friend, Mina Ashiro. Soon, life takes them in separate ways. While employed cleaning up after Kaiju battles, Kafka meets Reno Ichikawa. Reno's determination to join The Defense Force reawakens Kafka's promise to join Mina and protect humanity.

Yor and Loid may be keeping their true identities from each other, but telepathic Anya knows everything. Now, as they set sail on a luxury cruise, Yor must stop a group of assassins from reaching their target—while Loid struggles with a different mission altogether: figuring out what a good father is supposed to do on vacation.