It's a vibration collar. And it's only used in tartarus to train him to fight shadows and stay away from danger. There is no law in Japan that prohibits the use of sh- vibration collars in the dark hour, as far as I'm aware. How do you think Koromaru has been so obedient while we're fighting for our lives? Of course it hurts for you, you're weak to Zio, so you're overreacting.