Blue Sky City is overrun by the Red Caps led by Gauss. The operation "Snark Hunt" using human fear has been started involving citizens. Under the direction of Ryo's mother, Misa, who used to be a mercenary, Ryo and his friends are divided into three teams and aim for the enemy's control tower. However, unable to endure the outrageous strategy that used civilians, Hayato activates ARMS.