During the rise of the Demon Lord, humanity put aside its differences and came together to save the world.
After the war, humans began persecuting all demons, even those who didn’t align themselves with the Demon Lord.
They were effectively forced to go into hiding.18 years later, a young man named Rein trained alongside his childhood friend, Ciel.
They aimed to become imperial knights for their homeland, the aggressively expansionist Cedis Empire.
After venturing into a cave, a mysterious figure spirits Rein away and tells him,
“We have been looking for you, Demon Lord Diabolos.”