"D Genesis: Dungeon ga Dekita 3-nen" is a manga series set in a world where dungeons suddenly appear across the globe, fundamentally altering society. These dungeons, filled with monsters and rare resources, become central to the world's economy and power dynamics. The story begins three years after the first dungeon's emergence, focusing on the protagonist, Keigo Yoshimura, a salaryman who unexpectedly gains the ability to see the status screens of others, a skill typically reserved for adventurers who enter dungeons. This unique ability allows him to analyze and strategize in ways others cannot.

Keigo's life takes a dramatic turn when he encounters a mysterious girl named Yoyu, who possesses extraordinary combat skills and knowledge about the dungeons. Together, they form an unlikely partnership to explore the dungeons and uncover their secrets. Keigo's analytical mind and Yoyu's physical prowess complement each other, enabling them to tackle challenges that others cannot. As they delve deeper into the dungeons, they discover that these structures are not random but are part of a larger, more complex system with ties to ancient civilizations and otherworldly forces.

The narrative explores the societal impact of the dungeons, including the rise of adventurers as a new class of professionals, the economic shifts driven by dungeon resources, and the political maneuvering of nations and corporations seeking to control these powerful entities. Keigo and Yoyu's journey is not just about survival and exploration but also about uncovering the truth behind the dungeons' origins and their purpose. Along the way, they encounter various factions, each with their own agendas, from government agencies to rogue adventurers and shadowy organizations.

The series balances action, mystery, and world-building, with a focus on the evolving relationship between Keigo and Yoyu. Keigo's growth from an ordinary salaryman to a key player in the dungeon-centric world is central to the story, as is Yoyu's mysterious past and her connection to the dungeons. The manga delves into themes of adaptation, resilience, and the human drive to understand and conquer the unknown, all set against the backdrop of a world irrevocably changed by the appearance of the dungeons.