Lucifer Morningstar rules Hell with absolute calm and control, while Y/n stands beside her as one of the most powerful demons, equal in strength and feared by all. Their connection grows from cold understanding into something deeper, until they cross the boundary between Hell and the human world. As punishment, God strips them of their power and forces them to live as mortals on Earth. Decades pass, their bond changing into something real—only for them to be torn apart when they are sent back to Hell. Now, separated in the darkness, they must find each other again.