In a world thrown into chaos by the Demon Lord's return, Leona fights to stem the tide of empowered demons beneath an ominous red moon. Overwhelmed in battle, she is rescued by Hein, a determined researcher who reveals an unconventional method to counter the creatures' enhanced strength. Though reluctant, Leona agrees to entrust her body to his experimental approach, setting the stage for an uneasy alliance that could shift the balance against the encroaching darkness.