Rikka Isurugi has spent her life training in the ninja arts alongside her grandfather Hyoe, while following in the footsteps of her father, the respected researcher Allen. His work has resulted in a set of cutting-edge drones equipped with artificial intelligence and remarkable technical capabilities; although Allen intends to develop these drones for civilian use, others harbor more sinister intentions. On Rikka's 16th birthday, everything changes when a paramilitary group raids the Isurugi residence in search of the drone technology, killing Allen and Hyoe while Rikka manages to escape with the drones. Months later, Rikka is now an ordinary girl working as a private detective and sharing an apartment with another girl, Melissa. But when night falls, she dons her grandfather's fox mask and mercilessly hunts down those responsible for the attack. Driven by the anger she felt that day, Rikka will not rest until her family's killers receive the justice they deserve.