After the loss of his entire family in a car crash, Taiyou Asano tries to pull away from his childhood friend Mutsumi Yozakura, but she assures him she will not leave. Yet Taiyou becomes socially awkward and struggles to make friends at school, even though his persistent classmates keep trying.
One day the vice‑principal summons Taiyou to his office, only to threaten his life. A stranger takes him away and he awakens with Mutsumi, who introduces him to her siblings—a family of spies possessing superhuman abilities. Each generation produces one ordinary human who becomes the head of the clan, and Mutsumi is one of them; the family"s mission is to protect her with their lives.
The vice‑principal's real name is Kyoichiro Yozakura, the eldest son of the clan. He believes Taiyou poses a threat to Mutsumi, so the only way to keep both safe is marriage; the clan forbids killing within its walls. Though initially reluctant, Taiyou agrees to protect Mutsumi. Now he must train as a Yozakura spy to ward off the constant threats against both of them.
