The setting is a world where adventurers and monsters fight for entertainment that is recorded and broadcasted around the world. The MC is a black mage in the party of the 4th ranked hero party aiming to clear the Demon King Castle. However, he was kicked out by his party because they did not realise his debuffs were contributing to the party's success. After being kicked out, he was recruited by the Demon King to play the part of a monster and help defend against the parties trying to clear the castle. The Demon King is a hot girl who falls him almost immediately and he is surrounded by many cute monster girls in the Demon King Army. Meanwhile, his former party is struggling to fight without his debuffs and slowly realises the MC was actually critical to the party's success.