In the realm of the virtual game Cross Reverie, the unmatched power of the Demon King Diablo reigns supreme. Known for his rare artifacts and exceptional player level, Diablo crushes all who challenge him. Yet, behind this formidable persona lies Takuma Sakamoto, a socially inept gamer leading a reclusive life. His days are spent vanquishing feeble adversaries until a fateful summoning spell whisks him away to a parallel world, transforming him into Diablo himself. Welcomed by two summoners, Rem Galeu, a diminutive Pantherian explorer, and Shera L. Greenwood, a voluptuous Elf mage, Takuma finds himself bound to them after a failed Enslavement Ritual. Amidst the ensuing awkwardness, Takuma embarks on a quest with his newfound companions to nullify their contract, all the while adjusting to his unexpected role as the fearsome Demon King.