In a world where the conflict between humans and demons has continued since ancient times, Coral, codenamed , who has been raised as a spy since childhood, is entrusted with the important mission of infiltrating the Demon King's castle. However, due to the strategy of a certain person, the mission fails early on, and she is imprisoned in the Demon King's castle. What she saw there was the tragic end of the war caused by the magic rampage of Aries, the Demon King's son. If only she could redo this mission and prevent the prince's rampage... Wishing so strongly, Coral obtains the "Book of Time Travel," which allows her to go back to the past only once. What becomes newly visible during the re-do mission is the side of Prince Aries that he can't tell anyone about?!