A hundred and seventeen years ago, a demon offered a girl who was on the verge of death a deal. Having no other choices, she accepted and gained an almost immortal body. It was only when she got it that she discovered that immortality is nothing but solitude. For more than a century, she's been searching for clues to find him again, hoping that he can undo the deal. What will happen when she finds out the truth behind the deal? And will she fulfil her part of the deal?