Denka, Amaete Iikara Yamiochi Shinaide?

In a world where humans and demons have been at war for centuries, a spy trained from childhood is assigned to infiltrate the Demon King's castle. Her mission is compromised by someone else's manipulation, leading to her capture and imprisonment there. She witnesses the devastating conclusion of the war, triggered by the Demon King's son, Prince Aries, whose magical powers spiral out of control. Wanting to change the outcome, she acquires a time-travel book that allows one return to the past. As she relives the mission, she uncovers an unexpected aspect of Prince Aries that she must keep secret.