After folding his own startup, younger brother Yukio moves in with his sister-in-law Ai and her husband Kohei. On days when Kohei is away, Yukio discovers that Ai is unsatisfied with her marital life and begins feigning illness to skip work. He then starts tying her up and taking her by force. Though Ai initially resists, she gradually becomes drawn into the world of rope bondage. As a stark contrast to her ordinary life with her husband, a twisted relationship unfolds, showcasing Ai's profound transformation.