The female warrior Mai Hanano, who once fought against the Female Body Torture Research Institute, has since retired from active duty and lives a quiet life as an instructor within a spy organization. One day, she is visited by Chihiro Asai, a member of the Female Research Institute Investigation Division. Chihiro, who also has experience battling the Institute in the past, is struggling with a stalled investigation and asks Mai for help. Having left that life behind, Mai initially refuses. However, moved by Chihiro's intense gaze and determination, she confronts her former self and resolves to return to action. Mai Hanano's return to the Female Body Torture Research Institute marks the beginning of a new battle.