He is the prince of the Imperial Realm and was born to protect the Illusory Realm. He grew up to be able to protect the people he wanted to protect, but in the end he could not escape the fate of becoming a demon.
"I promised you that I would let you grow up well. If I can't do it, then I will have to destroy you!" The person in the Imperial Palace who was sworn to protect eventually became his enemy. Can the imprisoned soul find its true self?