Is it Your Nature to Kill?
It only took a few seconds for the Supreme to arrive at the Venomous Hill. The place was a home of different evil and vicious creatures that secretes venom. There are spiders, vipers, wasps, scorpions, snakes, and many more. Because of their venoms, the air in the place was also toxic for an ordinary person. Thus, it became forbidden.
With the toxic environment of Venomous Hill, it is enough for the creatures of Central Core to enjoy the place. But the citizens of this world invented a divine air that is poisonous to the devils. The air would make their internal organs slowly swell. The more they inhale the divine air, the more their organs well get swollen until it would burst and instantly end their lifespan.
It was the precautionary measure that the city made just in case the devils invade their world using their existing portals.