Yokai Magic

The concept of "Yokai Magic" is one isolated to Hisari, and is equivalently a nebulous one. When scholars from Keihatsu research Yokai of all forms, it is evidently clear even to a wandering sellsword that they wield a type of magic unlike mortal men. As a result, "Yokai Magic" became a catch-all term for magic that seemingly only Yokai or those of Yokai blood are able to use.
Initially, it was believed that only those of pure blood were able to use these magics. They were unteachable to ordinary mages, regardless of skill, and any Hanyou that attempted to ended up falling into madness. Over time, however, it became clear that Hanyou and other accursed were able to use these magics in small quantities. Utilizing this Yokai magic would accelerate their curse or alternatively embolden the fiendish blood within them, eventually turning them insane or overtaking their weaker mortal blood.
This naturally evolved into research dedicated to allowing normal mages to use Yokai magic. The research of this was banned at Keihatsu, and all documents and research notes related to it were either destroyed or locked away. No public reason was given for it, and all talk of learning Yokai magic became considered taboo.