Apollyon Rank

"The world's strongest, the apollyon rank. Yeah, never get caught on the bad side of one of these guys."
-Axel Navath
Apollyon is the 13th of the Order of the White Cross's magicka classifications. To qualify, one needs to have a minimum magicule PPS of 53,144,100, a total currently only held by 41 people around the globe. The apollyon rank is so powerful that a single individual holds enough magic power within their soul to level a city, theoretically giving them the attack strength of a nuclear bomb. As a result of this, every apollyon is automatically assigned to the S tier, regardless of ability or other external factors. 
Though all-powerful juggernauts on paper, in practice, they are not unbeatable. Like all mages, the members of the apollyon class may be constrained by knowledge, skill, ability to actually use their power, or mental blockage. This means that while difficult, they can be beaten by people in lower ranks than them, especially if they are in the S tier themselves, and can outmaneuver the apollyon mage.