Denka, Amaete Iikara Yamiochi Shinaide?

Synopsis

A world where conflict between humans and demons has continued since ancient times. 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 a certain person's scheme, the mission fails early on and she is imprisoned in the Demon King's castle. There, she witnesses the end of a brutal war caused by the Demon King's son, Prince Aries, going out of control with his magical powers. If only she could redo this entire mission and stop the prince from going out of control... Coral, who fervently wishes this, obtains the "Book of Time Travel", which allows her to go back in time just once. During the redo of the mission, she discovers a new side of Prince Aries that she cannot reveal to anyone!? (Source: Dbook, translated)