"Heheheh... You claim the title of Demon Overlord and yet do not know of me? Your ignorance knows no bounds!" The MMORPG Cross Reverie's top player, Takuma Sakamoto, is summoned to another world where he's forced to play the part of the Demon Lord Diablo! The next opponent standing in his way is the Demon Overlord! Sensing he might not win this time, Diablo visits the swordmaster to develop his skills as a warrior to break the limit of the races. Just as he does, the Demon Lord's army marches on the citadel city of Faltra! The adventurer Emile and the governor Galford take up their blades to do battle, but the strength of the enemy exceeds all their expectations!