A boy made a vow to another boy when he was young, but soon the other boy came to the capital to save his younger brother. Many famous doctors came to the capital. Many years later, that boy became the young master of the Demon Cult, but he met the boy who promised him the vow. However, he no longer had love, could not even control his thoughts, and would kill people randomly. The current emperor actually sent the boy who allowed him to experiment to catch him. Unexpectedly, a meeting in a prison made the current emperor fall in love with him at first sight.