@Wolfwhistler It was mentioned in one of the earlier chapter discussions
that Jaryuu is the real thing, but not because he's hiding his true power, but because for hundreds of years humans in the village near his cave feared him. In this world concentrated fear = evil magic power, and all of it was dedicated to him. However since he didn't believe himself to be Jaryuu the magic just floated around waiting for someone to claim it, which turned out to be Reiko who believed herself to be without a doubt part of Jaryuu.