A young woman named Miyako is hired as a maid at a secluded mansion where she meets another maid, the eternally cheerful and indestructible Mai. Tasked with caring for the mansion's owners and guests, Miyako quickly discovers that Mai has an extraordinary ability to heal from any injury, no matter how gruesome. This bizarre ability leads to brutal and sadistic treatment from the inhabitants of the mansion who use her regenerative powers for their twisted entertainment. Initially horrified by the violence, Miyako struggles to accept the house's cruel reality while attempting to maintain her sanity and ethics.

As Miyako delves deeper into the mansion's dark secrets, she begins to question the nature of pain, suffering, and human cruelty. The line between victim and perpetrator starts to blur, challenging her perception of morality. While Mai's resilience appears unbreakable, the psychological toll on Miyako grows as her empathy for Mai conflicts with her survival instincts. This tense environment creates a volatile dynamic that threatens to push everyone involved to the brink of madness.