In this world people were divided into two social classes. First one was Royals which was basically rich people born in good families and Rebels who had tendencies to act aggressive towards Royals. Royals to prevent that issue created special choker that hits then with electricity when they show signs of aggression. Rebels are obligated to wear it and the Science and Technology Royal Department gets a notification whenever choker is destroyed or taken off. Its also used to track the location of each Rebel.

One of the main issues with it was that this device often confused enthusiasm with aggression so Rebels were forced to stay stoic all the time.

One day Diluc went on a walk. He was a Royal. On his way he noticed a man that was pinning a woman to the wall behind her. He didn't have a choker so he was a Royal. But that woman...she did have one. Which meant she couldn't show any act of aggression towards that man otherwise she would get shocked with electricity and would take consequences of harming a Royal. It was obvious she felt uncomfortable right now. Diluc couldn't let that man harm her even though she was a Rebel.

Hey you! Take your hands off her