DxD: Shadow Monarch Novel

After defeating all monarchs for the second time and using the Cup of Reincarnation, Sung Jin Woo returns to his teenage form but faces an impossible choice. The Rulers warn him that his overwhelming power threatens to destroy his world and universe. They ask him to relocate to another universe where a planet similar to Earth exists, inhabited by demons, gods, yokai, angels, and fallen angels. Though reluctant to leave, Jin Woo agrees to protect his loved ones and the world he fought so hard to save. Seven hundred years later, on a distant planet, the beautiful silver-haired maid Grayfia Lucifuge receives a shocking system task: conquer the heart of the Shadow Monarch. Failure means the extinction of the entire demon race. As she stares in disbelief, Grayfia realizes she has stumbled into something far beyond her understanding.