Japanese ninja are often viewed as untrustworthy, yet they were in fact steadfastly loyal to their masters. However, in contemporary Japan, high school student and self-styled ninja Rekka Hanabishi struggles to uphold this legacy, until he rescues a cute girl named Yanagi Sakoshita from a gang of delinquents. Following the incident, Rekka judges Yanagi worthy of being his master and vows to protect her. As a gesture of mutual trust, the two share their most precious secrets: Yanagi possesses the ability to rapidly heal wounds, while Rekka can generate fire with a mere snap of his fingers. Yet, their striking exchange does not go unnoticed, as a mysterious woman known as Kage Houshi appears. She somehow knows of their powers and threatens them, asserting that Rekka must be returned because he is the only one capable of killing her. The pair stand their ground, but before the situation can worsen, Kage Houshi departs calmly. Believing the crisis has passed, Rekka and Yanagi resume their everyday lives, oblivious to the fact that they are about to be pulled into a centuries-old ninja conspiracy, with the lives of their friends and their own at stake.