After the sudden death of her husband, Reiko finds herself enveloped in loneliness and moves in with her late husband's sisters, Misuzu and Ayaka. The sisters warmly welcome Reiko as if she were their own family, but she becomes increasingly confused by their strangely intense sexual behavior. One night, Reiko witnesses the sisters passionately desiring each other's bodies. Overcome by an unfamiliar, burning longing, she begins to pleasure herself, seeking fulfillment in solitude. From that moment on, she is drawn deeper into the hidden world of desire known only to women.