6 Great Satans

The Six Great Satans (四大魔王, Yondai Maō) were the original rulers of Hell and the Underworld and leaders of the Devils. They were named Lucifer (Lucifuge), Beelzebub, Leviathan, Behemoth, Asmodeus and Nephthys.

Summary
At some point in the past, the six original Satans led the Devils against God and the Angels in Heaven as well as Azazel, Allen and the Fallen Angels in the First Holy War, the latter of whom retreated prior. The Six Great Satans eventually died in the Holy War after more than half of the 72 Pillars as well as a majority of the armies of Devils that serve the High-Class Devil Clans of the 72 Pillars were wiped out.

After their deaths in the Holy War, a group of the majority if the children of the Six Great Satans intended to carry on the legacy of their parents by gathering the strong supporters of the original Six Great Satans and finish what they started, the Holy War to realize the world domination ambition of the Original Satans. Their intention however, were opposed by a certain group of Devils and Demons, the Anti-Satan Faction, led by the descendants of the Six Great Satans, who wanted to ensure the survival of the Devils, Demons and Imps as a species, thus disapproving of the continuation of the Holy War. This dissension eventually caused a civil war to break out between the Devils and Demons which ultimately lead to the defeat of the Original Satans' children. Following the defeat of the children who were forced to retreat to the back parts of Hell and the Underworld, their names became titles for the new rulers of the Devils while the Original Satans became known as the Old Satans.

The current Satans are Dio Lucifuge (the current head of the House of Lucifuge), Sona Leviathan (the first child and daughter of the House of Leviathan), Seraph Beelzebub (of the House of Beelzebub), Fallnir Asmodeus (of the House of Asmodeus), Koma Behemoth (the elder brother of the current head of the House of Behemoth), and Kason Nephthys (the current head of the House of Nephthys), six Devils who were born with immense power, equivalent or superior to the original six and were chosen for the Satans' positions despite not being the official heirs of the original Satans.

Five of the children of the original Satans – Shalba Beelzebub, Katerea Behemoth, Victor Asmodeus, and Jackson and Orcus Nephthys – have allied with the Khaos House's Old Satan Faction, while Euclid Leviathan led the Magician Faction of the Khaos House, but no children or descendants of Lucifer allied with the Khaos House.

During the Second Holy War against Qlippoth, Trihexa and secretly, the Anti-Myth Faction, five of the six Satans sealed themselves with the legendary beasts, leaving Seraph as the sole New Satan remaining in Hell and the Underworld, with the son, sister and nephew of three sealed Satans filled their roles. The three new Satans are, Mephisto Lucifuge (the son and first child of Dio Lucifuge), Serafall Leviathan (the sister of Sona Leviathan), and Ocyrus Nephthys (the nephew of Kason Nephthys)

Trivia

 * All four of the current Satans (plus Dio, Sona and Kason) have legendary creatures in their group/peerage.
 * Each legendary creature and their master are:
 * Bahamut and Mephisto Lucifuge
 * Nessie and Serafall Leviathan
 * Kuyutha and Seraph Beelzebub
 * Basilisk and Ocyrus Nephthys
 * Ziz and Dio Lucifuge
 * Ōnamazu and Sona Leviathan
 * Falak and Kason Nephthys