WARNING: The following contains spoilers for Black Clover Chapter #281, “Assault on the Kingdom,” by Yuki Tabata, Taylor Engel and Annaliese "Ace" Christman, available now in English from Viz Media.
The Black Clover manga's latest revelation is a significant one in terms of devil history. Not only is the Spade Kingdom's dark connections with devil magic fleshed out, but also the inclinations towards hatred and fear among the Kingdom's current rulers.
Chapter #281 reveals that the legacy of hatred within the Spade Kingdom is connected to the birth of two ancient devils. These devils were once human mages from royal bloodlines who possessed powerful magic. At one point, they were friends, but jealousy drove them to hate each other and become devils.
The Dark Triad making pacts with devils to become devil hosts is no mere coincidence; this wouldn’t be the first instance of contact with entities from another dimension. Each of the Dark Triad members is also a descendant of the royal bloodline Zogratis, and they're the ones responsible for taking over the Spade Kingdom after defeating the former rulers, the Grinberryall.
Zenon now claims that the Grinberryall were protecting the ancient devils, but from who? Since the ancient devils were the manifestation of old royal mages, their bodies must hold magic unseen for many years. As the earliest known examples of mages becoming devils, their bodies likely hold secrets to the nature of the devil hosts, explaining why the Spade Kingdom is so inclined towards dark magic.
Devils derive their power from humanity's hatred. In order for them to create a union with a human, they must make a pact via ritual. The process of actually becoming a devil, however, has not yet been revealed in Black Cover. As such, finding out that two of the strongest ancient devils used to be humans is a huge deal because it means their hatred for one another must have exceeded human capabilities. It is still unclear if the ancient Spade mages were devil hosts at the time, but contracts with devils clearly have a price.
The Spade Kingdom may believe it can control devils with its vast knowledge of devil magic, but they're clearly just being used as part of the devils' own resurrection plans. Lucifero’s plan to bring the devils into the human world has been a long process, and these first two ancient devils might have been Lucifero's experiment to test the limits of hatred and jealousy. Although the devils are unable to manifest in the human world like Liebe, they can use the power-hungry subordinates of the Spade Kingdom to make their dreams into a reality.
Devils take advantage of human emotion and turn it into a power source, and it was manipulation by devils that led the two royal friends to became so jealous of each other that they eventually became devils themselves. It seems likely one of these friends was from the Grinberryall family, and the other from the Dark Triad's Zogratis family. Their intense hatred has been passed down for generations between the royal houses, and now, the Zogratis have taken full advantage of this situation.
Clearly, history repeats itself, and the cycle of hatred is only fueling the devils with more power in Black Clover. The Spade Kingdom certainly isn't the only kingdom with dark secrets. The two ancient devils are shown in Chapter #281 with bloody tears -- even as evil beings, they still feel pain and regret. Since they used to be human, there may very well be a method that can reverse their transformation, and the key to that transformation may lie in Asta and Liebe’s anti-magic capabilities.