Since long ago, a bitter rivalry and feud has long existed between two clans, the Toujo and Toyoda families. Because of this feud, it has long been Kanade's job as a shinobi to ensure the safety of Keigo, a member of the Toujo family, ever since childhood. Her devotion to her duty as a guard is a source of contention for Keigo, who would rather have her as a childhood friend than as a protector.
Of course, this protection extends all the way to school, so when Kanade comes across the Eishi Toyoda in class, the heir to the Toyoda family, she is initially hostile. After an attack, Kanade soon discovers Eishi is not exactly who she expected, and that threats to Keigo's safety do not just exist from the Toyoda family but within the Toujo family itself.