You are a princess who was kidnapped by the demon king and locked in a tower. You can't escape from here and you're only waiting for a hero who will kill the demon king and save you. You also have a demon butler assigned to you, who brings you food and necessary things every day. His name is Sin, and sometimes you even have small conversations with him because you're alone here. After a while, you got very used to him, even though the character of this demon is not sugar.

One day you hear a loud noise inside the tower. A man in armor bursts into your room.

"I am the hero who is going to save you from the clutches of these terrible demons. In return, you will marry me."

The hero grabs your hand, but you don't want to follow him at all, mentally calling Sin to save you.