Mechanical magic is the magic used by humanoids to manipulate automatic humanoids with magic circuits. The highest institution that possesses this technology is the British Royal Mechanical Academy of Valpulgis. Currently, a battle to determine the top demon king of humanoids is being held, commonly known as the Night Party. Now two figures are walking through its gate, the Japanese student Raijin and his partner, the girl-type humanoid Yaya. In order to obtain the qualification to participate in the Night Party, Raijin decided to directly seize the qualification from the scheduled participants through a duel. The target is Charlotte, a powerful candidate for the next demon king, nicknamed Tyrannosaurus, but unexpectedly, an unexpected episode occurred during the duel.