The Divine Purge

Once a year, angels descend from Heaven to attack sinners in Hell. This day is known as the 'Divine Purge'. It comes from a deal between Satan and the ruler of Heaven, where sinners would not have to suffer in Hell as long as the angels were allowed one day to kill off as many sinners as possible. The reason for this was because Heaven is powered off of the suffering of sinners.

On this day, angels are allowed to kill anyone they please. This includes Blackwell students, if they manage to break through the school's thick outer walls. If an angel manages to get their hands on a sinner, they don't actually kill the sinner (as that would result in the sinner just respawning back to safety outside of Hell). Instead, the angel stabs the sinner with special electrical weapons they are provided with beforehand. These weapons are extremely painful and hard to take out once stabbed. These weapons collect the sinner's suffering as well as their souls, thus sending power up to Heaven. After having their soul removed, the sinner melts away and becomes dust.