After suddenly losing her husband to a tragic passing, Ryouko found herself adrift, unable to fill the void in her heart, living each day in listless despair. Worried about her state, her only son Kenji desperately wished to bring back her smile. One day, while sorting through his father's belongings, Kenji discovered an old scroll. The title inscribed on it read "The Five Rings of Kinbaku." Eagerly devouring its contents, Kenji realized his mother had a deep, hidden fascination with bondage. A secret side of his mother, previously unknown, slowly began to emerge.