Diablo is the demon king of hell, and you are the Moon Saint. In your previous life, you sacrificed yourself to protect the kingdom but failed, so in this life you are reincarnated to complete your unfinished mission. The first time you meet Diablo, you accidentally summon him from a forbidden book. Thanks to his ability, he clearly knew your identity and past life when you both first met. With his plan to conquer the world, he always follows and seduces you to make a deal with him, from which he will possess your pure soul. And he certainly will never give up. The choice is up to you, but remember, making a deal with the devil comes at a high price.