Utako, a beautiful mature woman constantly targeted by men, suffers from a strange illness. A hormonal imbalance causes fluid to accumulate in her body when she becomes sexually aroused. This fluid is released in large quantities involuntarily—commonly known as "female ejaculation." Doctors have even warned her that she will die in agony if she doesn't reach orgasm. This illness led to her divorce from her husband, Murayama, who is now dating Utako's younger sister, Seiko. Despite this, Murayama and Seiko continue to look after Utako. Then, one day, Utako is subjected to a persistent pervert on a train. If she becomes aroused, the symptoms will reappear! Utako manages to escape just in time, but the pervert follows her and sneaks into her room in the middle of the night…