Isaku Senagaki grew up inside a yakuza clan after her parents died in a car accident when she was five, raised by her gangster grandfather and shadowed ever since by Keiya Utou, the family's devoted 26-year-old guard dog. When Isaku finally gets her shot at an ordinary high school life, Keiya enrolls right alongside her, chain-smoking and armed, determined to protect her from bullies, bad influences, and anything resembling a boyfriend.