Saki lives in an apartment with her brother-in-law and his wife, along with the husband's younger brother. Unlike her diligent, career-focused brother-in-law, the younger brother is a quiet middle-aged NEET who harbors abnormal sexual feelings toward his sister-in-law Saki. One day, he accidentally sees Saki drenched by a sudden downpour, her clothes soaked and clinging transparently to her body. The moment he sees her, something inside him shifts. The cold wetness of her clothes drains his body heat and shatters his rationality, plunging him into an abnormal state. Gradually, he becomes aware of his own rising body temperature, drawn uncontrollably into the memory of that incident, unable to comprehend his own desires.