Holy Knights

The Holy Knights (聖騎士 Seikishi) are the most powerful knights in Britannia who are heroes that protect the kingdom. They are a group of terrifying individuals, with each able to match an entire country's army in strength and power, and having magic that transcends human knowledge imbued within their bodies.

In Britannia, there are orders of Holy Knights within the kingdoms of Liones, Danafor (prior to its destruction) and Camelot.

10 years ago
When the Seven Deadly Sins were framed for killing the previous Great Holy Knight, Zaratras, and plotting to overthrow the kingdom, the entire order of Liones' Holy Knights were dispatched to kill them all. After the group of knights' supposed offense and the subsequent escape of at least four of them, the Seven Deadly Sins were dissolved and were relentlessly hunted down by the Holy Knights.

Present day
King Bartra Liones, although realizing that a predicted Holy War would soon occur, ordered all the Holy Knights to lay down their weapons in an effort to avoid war. However, the Holy Knights, believing that the war was inevitable and that protection of the kingdom was their duty, captured the king a few days in a successful coup before Elizabeth found Meliodas, and began military preparations. The kingdom, now under the command of current Great Holy Knights, Hendricksen and Dreyfus, fell into a state of distress as citizens from towns and villages surrounding the kingdom were enslaved or forcefully recruited into joining the military effort: the men forcibly trained as soldiers, the women and children forced to amass food for storage, and the elderly forced to construct castle walls. Death has now become the penalty for insubordination under the rule of the Holy Knights, with them justifying their enslaving of the citizens with the fact that the war is being fought for their protection to begin with.

It is revealed that Hendricksen plotted to resurrect the long-sealed Demon Clan so there will be a formidable enemy for the Holy Knights to fight and win the Holy War with aid from the New Generation Holy Knights.

During the Sins' infiltration and Arthur's surprise visit, the Holy Knights were divided as several members began to question themselves if protecting or oppressing the people is their role and eventually turned against their fellow comrades.

After the king of Liones was successfully rescued and Dreyfus admitting his crime of murdering Zaratras, Hendricksen who recently recovered from his defeat by Gilthunder, triggered a spell that causes the demon blood of the New Generation Holy Knights to run out of control and mutate them into hybrid Demons, thus causing chaos and confusion among the Holy Knights and knights throughout the kingdom's capital.

The Holy Knights immediately fought against the New Generation Holy Knights-turned-Demons throughout the capital in defense of their kingdom but began suffering heavy losses among their ranks in multiple skirmishes.

Holy Knights of Liones
Protectors of the Liones Kingdom; the Holy Knights prepare for the prophecized Holy War led by the Great Knight usurpers who felt the King’s benevolence would be the destruction of the kingdom. Frightened by an unknown enemy, they work the populace to their deaths so as to save them from a fate that may ultimately be nothing more than superstition.

Holy Knights of Danafor
The faithful knights of Danafor defended their kingdom until its last hour, but tragically fell before the might of the Dragon’s Sin, who had lost himself in his wrath. The few stragglers left fight on in Danafor’s name, but are ultimately lost without their homeland.

Great Holy Knight
The Great Holy Knights are the most powerful of of the Holy Knights, and possess the authorities of commanding over them, thus making them the leaders of the Holy Knights. This gave the current Great Holy Knights, Dreyfus and Hendricksen, command over the whole country after the coup d'état.

Holy Knight
The Holy Knight is a title given to well established knights that have great strength, which is equal to that of an army. They have command over ordinary knights and train apprentices to become full fledged Holy Knights. All of them are imbued with extraordinary powers, such as Gilthunder's lightning abilities and Guila's explosion abilities.There are titles within the Holy Knight themselves, it seems the higher ranked they are, the more power they have, these titles are:
 * 1) Cardinal
 * 2) Diamond
 * 3) Platinum

Apprentice Holy Knight
Apprentice Holy Knights, as their name suggests, are apprentices and disciples of existing Holy Knights who are undergoing training to become seasoned and qualified Holy Knights. They are fairly powerful compared to ordinary knights, whom they have authorities to command over, but are still much weaker than a Holy Knight.

Reactors
"Reactor class" Holy Knights, also called "reactors" and "demon reactors", refers to any Holy Knight that drank, and is compatible to, demon blood. After the blood has been ingested, those who are compatible gain new powers and have their strength greatly increased. They fall under one of two categories:

Old Generation
Prior the creation of the New Generation, the Great Holy Knight, Hendricksen, tested the Demon blood on a selection of Holy Knights. However, the outcome was a failure as they were uncontrollable and their powers were extremely unstable.

New Generation
Instead of compelling Holy Knights to consume the blood, Hendricksen experimented with Holy Knight apprentices. Although they were relatively less powerful that full-fledged Holy Knights, they were more compatible with the blood and could retain their self-control. The rest of the Kingdom of Liones, not knowing the cause of many knights suddenly gaining great powers, has dubbed them as the New Generation.

Trivia

 * Holy Knight is a special job class in Final Fantasy Tactics for the PlayStation.
 * The practice of the current Holy Knights ingesting demon blood in order to enhance their powers is very similar to the Grey Wardens drinking Darkspawn blood in the RPG series Dragon Age.