Kurenai—the legendary mercenary who dyes battlefields crimson. Having completed missions on numerous battlefields, the new duty assigned to him is "to become a teacher at a Japanese high school." Taking on the name Shota Echizen, he heads to Japan. When he learns the details of his assignment, it was "to protect a female student named Sakurako Kujo who attends the academy." For him, who was raised on the battlefield and has never had dealings with women, can he possibly carry out this mission, more difficult than any other—?