The Demonic Disturbance was a city-wide invasion on the capital of the Re-Estize Kingdom by an army of demons led by Jaldabaoth. Unbeknownst to the kingdom and the rest of the New World, the attack was actually orchestrated by Nazarick as part of Operation Gehenna.
A small war had taken place within the kingdom, between the Re-Estize Royal Family led by Princess Renner and the criminal organization, Eight Fingers. The princess's aim was to save her kingdom by expunging Eight Fingers who had been responsible for most of the country's major crimes. To accomplish this, Renner had brought in like minded individuals to her cause and hired Adventurers, such as the Adamantite-ranked Adventurers, Blue Roses. The two forces were seemingly locked in a stalemate until the forces of Nazarick were involved into it.