Reiji Takahashi is a Special Operations Agent. While in the middle of sweeping through a criminal group's warehouse, he finds Nina, a victim of a trafficking ring dealing in child assassins named "Dolls." One thing led to another, and he ends up being assigned with caring for the young assassin (Who, coincidentally, is aiming for his life).

Can Reiji, a man with absolutely zero experience with children, become a proper father to this tiny assassin and teach her how to lead a normal life? Find out in this heartwarming childcare comedy between a "hard-boiled" operative and his adoptive(?) daughter!