When you enter The Reigon Of Legends, you are turned into your Aura Beast. That is a side-effect of becoming a Haru-Human Hybrid. Your Aura Beast is different based on your peronality.
The Aura Spirit is a being within all, that takes a physical form of your personality. When you fuse with Haru, your Aura Spirit does as well, and becomes an Aura Beast.