In the MMORPG Cross Reverie, Sakamoto Takuma was so strong that the other players called him the Demon King because he was so strong. One day, when he shows up in the game, he is called to another world. There are two people who say, "I am the real summon master." The girls cast a spell on Takuma that turns summoned beasts into slaves. But a strange ability called "Magic Reflection" is used! The girls were the ones who were turned into slaves. Takuma was bewildered. He is the best magician, but he doesn't know how to talk to people. When he was scared, the first words that came out were the ones he used when he played the Demon King in the game?! "I'm fantastic you say? I'm sure I am. I am Diablo. People fear me because I am the Demon King." This is the story of the Demon King's (acting) adventure in another world, which he plunges into with all of his strength. Raise the curtain!