Afflicted with a heart condition, Meiji-era noblewoman Satoko is determined to secure a marriage that will benefit her family before she dies. But before she can realize her goal, she's targeted by a mysterious assassin named Shinpei. In a last-ditch effort to save her life, Satoko asks her would-be murderer to marry her. Her proposal isn't sincere, but unfortunately for her, Shinpei loves as intensely as he kills. Can Satoko find a way to break the engagement without losing her life?
Satoko's bodyguard, Kotaro, comes to her rescue at last, but Satoko can't quite bring herself to celebrate. If she leaves now, it means saying goodbye to Shinpei, the assassin who has saved her life time and time again. Making matters worse, seeing Satoko with Kotaro ignites a fierce jealousy in Shinpei that drives him to challenge Kotaro to an explosive showdown! As the two men clash, the truth behind Satoko's kidnapper comes to light.