Nobuo Koyama is the father of Kadode Koyama, one of the two main protagonists of the series. He works as a manga editor, a profession that places him within the creative industry of Japan. On August 31, the day an enormous alien mothership first appeared over Tokyo, Nobuo happened to have the day off and was at home with his family. He told them he was going to check on what was happening at his company and left the house. After that, he never returned, and no one knew where he had gone. His sudden and unexplained disappearance becomes a lingering absence in his daughter’s life, shaping some of her emotional experiences as the story progresses.

As the narrative unfolds, it is revealed that Nobuo did not simply vanish; he was captured by the National Justice Headquarters, a government organization involved in managing the alien crisis. With the assistance of an ally who made a heroic sacrifice to create a distraction, he managed to escape. Later in the story, he becomes an active participant in the larger conflict, eventually undertaking a journey through time in an effort to avert the extinction of humanity. This time travel attempt indicates a fundamental shift in his character from an ordinary father and office worker to someone willing to take extreme measures for the sake of his family and the world. His motivations are rooted in a sense of responsibility and love for his daughter, as well as a desire to correct the catastrophic course of events. Throughout the series, his development traces a trajectory from a missing person to a key figure in the secret struggle surrounding the invasion, demonstrating resourcefulness and determination despite lacking any special abilities or combat training. His relationship with Kadode remains emotionally central, defined by separation and the eventual hope of reunion, even as the circumstances grow increasingly surreal and dire.