Ruth Kaisel grew up being looked down upon since childhood because his mother was from a red-light district. He joined the Imperial Knights to run away from those who did not recognize him as a member of his father’s family but eventually became the leader of the knights at a young age due to the power of that same family, despite not being able to free himself from his father’s family no matter where he ran. He found himself serving the royal family as the escort of Crown Prince Ail, who was beautiful and elegant with dazzling red hair but was extremely eccentric and selfish. After some time of being overwhelmed by the young prince, Ail urges Ruth to become his 'true shield' in the castle and fight a silent but deadly battle within the palace walls. Due to threats from those close to him, Ruth begins to play the role of a terminally ill lover, while following orders. Fake lovers who started with the purpose of using each other, but ending up in a complicated relationship. Will the only thing left be the pain in their hearts or will they finally feel the joy of freedom?