There's another side of Japan that carries non humans, where a royal family rules over all monsters. One secret is that the royal family has a child, growing up in the castle reading novels and training to be the next ruler after his father.
Now that he turns into a senior, his parents gives him a chance to experience how it feels to be out in the open and meet new people. But his identity remains a mystery to the outer world for him to be protected.
~Will this secret remain until than?
~Who is the hidden child?
~How strong will the prince be until he rules over?