Ten Commandments

are an extremely powerful group of elite warriors and the strongest amongst the Demon Clan. Handpicked by the Demon King himself, each member possesses a, a unique power gifted to them by the Demon King, which delivers a unique curse to whomever breaks a rule specific to each member. This power is absolute; it cannot be opposed even by its wielder. The curses will only be lifted if the victim defeats its wielder or at the victim's death.

Overview
Three thousand years ago, the Ten Commandments fought for their race against the other four races (goddesses, giants, fairies, and humans) in the great, ancient war but were defeated and sealed by the Coffin of Eternal Darkness but Fraudrin somehow managed to avoid being sealed and sought ways of releasing his people for centuries, until the present day, when he was able to manipulate Hendrickson into freeing the other nine members from the seal (as he did not have enough of Elizabeth's blood to break the seal completely).

As they were completely drained of their magical powers by an after effect of the seal, the Ten Commandments elected to head towards Edinburgh while leaving a terrified Hendrickson behind. Arriving at their destination, they were surprised to find a a castle in ruins, and a giant hole bored into the land. Zeldris deduces that the hole was made by Meliodas, but they had no way of knowing the castle was destroyed by Escanor.

Their presences in Britannia awoke two of the Demon Clan's Albion, one at Camelot and the other at the Fairy King's Forest, which were destroyed by Meliodas and King. Sensing the Albions' destruction, Galan was delighted to know that there are still powerful people even in the current age and decided to take action despite them still having yet to recover their full power. He traveled all the way to Camelot in 72 high jumps and encountered three members of the Seven Deadly Sins. He easily overwhelmed them and annihilated almost half a portion of Camelot and its citizens and slaughtered its Holy Knights in battle. However, Gowther's power Invasion deluded Galan about having killed Meliodas, Diane, Slader, and Merlin.

Later on, the Commandments continued to rest and recover their magical power through eating the souls of humans they devoured and were shocked when they sensed Meliodas regain his full demonic powers at Istar.

Suddenly, Meliodas appeared out of nowhere through Merlin's teleportation and casually greeted the Ten Commandments who were surprised by his sudden appearance. Zeldris and Fraudrin were going to attack him but Galan told all of them to stay out of it as Meliodas is his prey to kill. Melodias battled and defeated Galan in less than ten seconds before warning Zeldris that the Seven Deadly Sins will defeat the Ten Commandments with everything they've got, warning them of their doom if they stepped out of line.

In response, Zeldris and Fraudrin attempted to attack Meliodas from both sides, but he was teleported back to Istar. Galan was angered and humiliated by his defeat at the hands of the "Accursed Demon".

As Galan complains and demands that Merascylla find Meliodas he is cut off by Zeldris as he tells him and the other demons that their goal is the domination of Britannia and commands the others to move out in groups of two (or more) in order to recover their magic power as quickly as possible and to use whatever methods they deem necessary to eradicate the other four races. Fraudrin then asks if this was a declaration of war against Meliodas which he reply's saying that this isn't war but an extermination.

Still angered by his defeat and the thought of Meliodas being "beyond" him, Galan tries to clams to have been able to defeat Meliodas any time he wanted, however before he can finish his sentence he is stopped and warned about lying by Dolor, questioning if he had forgotten that the Ten Commandments would incur their own curses on themselves if they break their own laws. Galan then lowers his head in response but still curses Meliodas in his mind. The Ten Commandments then disperse, Zeldris and Estarossa, however, remain behind.

Derrierie and Monspiet arrive at the town of Bellford where they promptly eat many people's souls. Dolor and Gloxinia arrive at Vaizel at the construction site of a new "brawl colosseum", because Gloxinia finds the site and activities surrounding it interesting. Meanwhile Fraudrin arrives at the town of Ferson, where he is promptly attacked and seemingly defeated by members of the Pleiades of the Azure Sky, and then taken to the a research tower in Zeldon, while Gray Lord watches. Meanwhile, Merascylla, who teamed up with Galan, begins to resurrect the dead all over Britannia in order to wipe out the living people.

Upon noticing that one her zombies is resisting her magic, Galan and Merascylla arrive to see what is happening, from there a great battle ensues between them and Fox's Sin of Greed Ban and eventually Lion's Sin of Pride Escanor which ultimately results in their defeat and possible deaths. Dolor notices this, as well as what happened to Fraudrin, and relays this to his partner, as they patiently wait for all the unsuspecting prey to arrive at the "Fight Festival" they are holding to draw strong souls to them as a more efficient way of recovering their lost magic power.

Meanwhile, Fraudrin is being held captive by the Pleiades who intend to prove that humanity can best the ancient demons and even defeat a member of the legendary Ten Commandments. Fraudrin then reveals that he is not a "real" member of the Ten Commandments, but a replacement for the missing member, Gowther. Gray Lord then appears, disquised as Dogget to retrieve Fraudrin. Denzel Liones, the leader of the Pleiades, lets them leave being cautious of Gray Lord's commandment. Fraudrin and Gray Lord then walk out, with Fraudrin stabbing Deldrey in the gut as revenge for their last battle. Before going, however, Fraudrin questions why he is leaving them alive, blaming his time in a human as making him soft, and decides to kill them all and destroys their base. As it crumbles, Fraudrin and Gray Lord leave, ready to continue their mission. They are later seen resting in a cave.

Dolor and Gloxinia decide to organize a Great Fight Festival as an efficient way to gather strong souls together. Meanwhile, Derrierie and Monspiet have completely wiped out the populations of nine cities and towns in northern Britannia. Estarossa and Zeldris apparently parted ways at some points, as Zeldris went on to conquer Camelot's royal capitol single-handedly.

Dolor and Gloxinia's festival is short-lived, as they are unexpectedly attacked by a participant whose power suddenly spiked tremendously. Afterwards, Meliodas attacks them both, and despite their best efforts, it seems he is going to kill them. But, before he can finish them off, all of the other Commandments (except Galan) arrive to aid them. After a grueling battle, in which Merascylla is killed unexpectedly by Ban, Estarossa seemingly kills Meliodas, and the eight remaining Commandments set out to solidify their conquest of Britannia.

A month after Meliodas' defeat, the Ten Commandments have Britannia under their thumb. They send out squads of lesser demons to terrorize people and stamp out any resistance and it has become common practice to sacrifice Holy Knights and other with strong souls as a form of appeasement. Some people do this to protect themselves and their families while others do it out of genuine adoration of the Ten Commandments.

Trivia

 * The "Commandments" from which the group's name is derived, all seem to be loosely based on one of the real Ten Commandments from the Abrahamic religions.