Rikka Isurugi descends from a line of ninja but would rather follow her father Allen, a robotics scientist, than her grandfather Hyoei into the family trade. On her birthday a hit squad led by Allen's former colleague Lauren storms their home outside Brad City to seize his research. Allen's three AI drones (the eagle Kasumi, the dog Oboro, and the flying squirrel Madara) carry Rikka to safety, and she vows revenge, taking up the masked ninja mantle of Black Fox.