A story idea that i came up with one night. No idea if it would work out or not.
The Heavenly Demon Apollyon. He ended up being captured by five different races who did a ritual to lock him in the heavenly void. For five hundred years he would be trapped there being forced to watch his own death on loop but each time the loop restarted the death would become more brutal than the last. During that time he managed to do two things. The first thing that he managed to do was form a stronger will called the absolute will. This means that all forms of mind attacks will fail against Apollyon. The second thing that he managed to do during that time was cultivate his heavenly energy enough to connect to the cosmos itself and form infinite energy for himself to use. When he managed to do these two things he ended up shattering the restraints he was put in before distorting space and shattering open a cosmic rift into the mortal domain. When he descended upon the mortal domain he made himself known by releasing a large amount of heavenly energy covering the entire mortal domain. This was a warning telling the five races that they made a mistake and they will pay for what they have done.