In the MMORPG Cross Reverie, Takuma Sakamoto is so powerful that he is lauded as the “Demon Lord” by other players. One day, he is summoned to another world – but with the same appearance he had in the game! There, he meets two girls who both proclaim themselves to be his Summoner. They had performed an Enslavement Ritual to turn him into their Summon... but that's when Takuma's passive ability <> activated! Instead, it was the girls who had become enslaved! Though Takuma may have been the strongest Sorcerer there was, he had no idea how to talk with other people. That's when he makes his choice: to act based on his persona from the game! 

“Amazing? But of course... I am Diablo, the being known and feared as the Demon Lord!” 

So begins a tale of adventure with an earth-shakingly powerful Demon Lord (or at least someone who acts like one) taking on another world! 

(Source: J-Novel Club)