Thirteen Calamities

The Thirteen Calamities (自然破壊 (サーティーン・カタストロフ), Sātīn Karamitiesu lit. Destruction of Nature) are thirteen extremely powerful demons that were sealed during the climax of the Dragon Civil War, each currently residing within one of the countries within Earth Land, under their own unique seal specifically made for them.

Overview
The Thirteen Calamities existed during the Dragon Civil War, and upon the ensuing chaos, took advantage of it in order to cause create destruction in their wake. They were extremely powerful, and were difficult to destroy for good, being believed to have been immortals. However, soon after, they were sealed away, each beneath a country of Earth Land, with only Desierto having no demon within it.

The power of the Demons is measured by the power of the seals used on them, and each seal's power uses the power of all the citizens existing within said country. As such, the citizen are unknowingly being the fuel to the Demon's seals, and keeping them difficult to shatter. However, this also means that the country's size is also a major factor, as the larger the country, the more people are present to grant the seals power, which in turn, measures the power of the Demon sealed within it. In short, the larger the country, the more powerful the Demon.

They do not possess a leader, or are an official organization, but a group of demons with the common goal of spreading chaos, that left a small, but known dent in the history of Earth Land. Along that, they were all from different backgrounds, some even mistrusting each other, or being related in someway, such as siblings or lovers.

Seals
The seals used on the Thirteen Calamities lock the demons in a form of "stasis", leaving them stuck, outside of "time", the same way they were the moment they were sealed. And since centuries have passed since they were sealed, the seals only grew more powerful than they were originally, thanks to the years of power they absorbed from the people of the world.

In addition, each seal was made specifically for each demon, made as an antithesis to them. And if broken, the seals would have an additional, detrimental effect on the Demons. A prime example being Deviot's life force being slowly drained from him after being freed by Marx, or Carmina's seal, which completely removed all of her powers from her, and granting her a frail, humanoid form.

Azazel claims that each seal has a complex "rune system" that needs its own unique "key" to unlock. Azazel spent merely 10 years working on a key for Deviot's seal, while Carmina's seal was broken by Deviot, due to their seals being similar in terms of their "system", and Deviot being Carmina's brother. He also hypothesizes that the seal of Pregrande Kingdom and Minstrel are the most powerful, and will be the most difficult to break.

Strength
The Thirteen Calamities were powerful Demons, and by today's standarts, are said to have been on par witht he likes of an S-Class Mage, or even a Wizard Saint. In addition, they are rumoured to have been immortal, further supporting the fact that killing them for good was considered difficult, and were forced to be sealed instead. However, it became apparant that only few possessed this "immortality", and that it was infact merely their power that made them difficult to kill, while others simply possessed incredible regenerative ability.

However, after being sealed away from centuries, their power also depleted, as evident by Deviot being incredibly weakened after his release, and would have required time to regain his full power back. As such, while still incredibly powerful, even when weakened, the Demons will still require some time in order for their full power to return.