"His Dungeon Exploration Partner Is a High School Girl!?" Masato, the eldest son of the Jingu family, begins working as an explorer in the "Tokyo Dungeon" to support his younger brothers after their parents pass away. However, realizing the limits of working alone, he decides to look for companions to help conquer the dungeon. That is when his younger brother Rekka introduces him to Tachibana Rika, and the two form a party together. They encounter many hardships along the way, but as they support each other and overcome those challenges together, their bond gradually grows deeper...!?