Jinyou in Touhou
Becoming a jinyou is considered to pose a grave threat to the balance of Gensokyo, enough for Reimu Hakurei to call it "the greatest sin of all" and to actually kill jinyou rather than defeat them non-lethally like most youkai. The exact reason for this has not been explained, but may be related to jinyou learning secrets about Gensokyo to which the Human Village is not privy, to jinyou having different values from normal youkai, or to the risk of Gensokyo's youkai numbers becoming too great for its human population to sustain.
Exactly what constitutes a jinyou is unclear. A human can transform themselves into a magician youkai by using magic to suspend or replace their bodily functions, yet magicians do not seem to be considered inherently dangerous. It may be that jinyou use more foul or taboo transformation methods than magicians (the jinyou who appears in Forbidden Scrollery being essentially a stabilised vengeful spirit), that becoming a magician - which requires decades of study - is too difficult to appeal to large numbers of humans, or simply that there are no magician youkai originating from the Human Village. Likewise a number of major characters (including Sakuya Izayoi, and even Reimu herself) have been described as "youkai-like humans" at times, but it is unclear if they fall under this definition, particularly since few of them live in the village.
Characters under this Bestiary