Nanako Shichigusa, a 16-year-old hospital maid, serves under a scientist conducting clandestine experiments. Though tasked with domestic duties, her clumsiness and accident-prone nature contrast sharply with the facility’s cutting-edge research. Bound to the hospital by a familial debt that sold her into servitude, she endures grueling physical conditioning and harsh discipline from the lead scientist, framed as preparation for an undisclosed future experiment.

Her genetic code harbors rare regenerative properties tied to Project "GREEN," a classified initiative drawing attention from military and religious factions eager to manipulate its evolutionary implications. Flashbacks suggest a generational link to the scientist’s lineage, with predecessors mirroring her appearance and role—hinting at cloning or engineered replication. Connections to Nana-Go, a prototype cyborg, further unveil her origins as a covertly engineered subject designed to awaken dormant abilities tied to her DNA.

Despite facing mutated creatures, hostile operatives, and experimental failures, Nanako’s loyalty to her manipulative overseer persists. Her perceived ineptitude belies an uncanny capacity to inadvertently catalyze critical events, weaving vulnerability with quiet influence. The scientist oscillates between callous exploitation and protective intervention, their fraught dynamic underscored by fragmented memories of a shared childhood and ancestral ties.

As the series unfolds, revelations about her genetic singularity and historical entanglement in the experiments emerge, yet her ultimate fate remains unresolved. Her narrative lingers in the liminal space between expendable pawn and indispensable key—a duality fueled by the latent power within her biology, which fuels both scientific ambition and escalating external conflicts.