In the bustling town of Edo, the kunoichi Ruri Hanabusa works as an assassin to earn the money needed for her sister Murasaki's medical treatment—but she's been failing time and time again. One day, she receives a high-paying contract worth 100,000 Ryo, but the target is none other than the Shogun of Edo, Tokuyama Tenrai. Determined, Ruri steels herself and accepts the mission. However, the Shogun's stronghold—Edo Castle—is filled with traps at every turn, set by the genius and cold-hearted tyrant who's known as both a brilliant mechanical engineer and a ruthless ruler... Will Ruri survive and succeed in her deadly mission, or will she be the next to fall?