Time has passed since the summer adventure that saved both the Digital and Human Worlds, and the number of children with partner Digimon has steadily increased across the globe. However, this new and unique nature has cast a looming shadow, as many of these children face persecution and the threat of being targeted for military use. The original DigiDestined, now grown, find themselves at the center of a new, invisible war to protect these kids.

The central narrative arc follows Taichi Yagami and Yamato Ishida, who are working directly on rescue missions for children in danger. During one such operation, they are suddenly ambushed by a mysterious and aggressive Digimon, forcing them to fight with their trusted partners, Agumon and Gabumon, once again. This event triggers a broader recollection of untold battles and a period of great turmoil that occurred between the defeat of previous villains and the peaceful, utopian future seen in the epilogue of Digimon Adventure 02.

The narrative is framed by the author Takaishi Takeru, who is seen writing the next chapter of his long-running series of books about the DigiDestined's adventures. He explains to his partner Patamon that this new volume is about the very events that led him to start writing the series in the first place, creating a reflective and personal context for the chaos that follows. The story then expands into a montage of simultaneous conflicts, showcasing that the struggle was not isolated to Taichi and Yamato. All the original chosen children, including Sora Takenouchi, Mimi Tachikawa, Koushiro Izumi, Joe Kido, and Hikari Yagami, are shown fighting manifestations of darkness and unknown mechanical enemies in various locations around the world.

Notably, the second generation of DigiDestined from Digimon Adventure 02 also play a significant role. Motomiya Daisuke, Ichijouji Ken, Inoue Miyako, and Hida Iori are depicted leading vast armies of Armor Digimon, including previously unseen forms that utilize various Digimentals, suggesting they have gained greater mastery over their powers. These scenes feature Iori commanding aquatic forms, Ken leading flying Digimon, and Daisuke charging on land alongside a herd of armored creatures. Their involvement highlights a global and coordinated effort to push back against the mysterious threat.

The setting shifts rapidly between the real world and the Digital World, with key locations including a car chase in Northern Europe, a hospital in Kanagawa, Aomori prefecture, and various digital landscapes. The narrative establishes that the battle never truly ended for the DigiDestined, even as they grew into adulthood. Taichi and Yamato, accepting this reality, ultimately evolve their partners into their most powerful forms, War Greymon and Metal Garurumon, to face the unknown future. The project serves as a visual epilogue, filling in the narrative gap between their young adult lives and the peaceful world where every human has a Digimon partner, celebrating the enduring bond between the children and their digital monsters twenty-five years after the original adventure began.