Takuma Sakamoto, renowned as the "Demon Lord" in the online game Cross Reverie, is unexpectedly pulled into a parallel universe with his game avatar intact. There, he is confronted by two girls who claim to have summoned him through an Enslavement Ritual. However, to their surprise and Takuma's power, he in turn masters them with his passive ability. Despite his reputation as a powerful wizard, Takuma struggles with socializing, and adopts the persona of Diablo, the feared Demon Lord, to venture out with his new companions on a thrilling adventure in this unknown realm, employing his earth-shattering powers.