@ShinyDiamond: That rule always bothered me...I mean, is interaction between the players somehow not considered contributory to the game as a whole? Anyway...
The possibility of a human getting to the academy depends on how the races cross realms. Do Youkai just poof about? Is there a particular ritual for a particular day that could have been accidentally triggered? Are there designated portals between the worlds? That question needs to be answered first.
Besides the merely practical reasons, a human in Youkai world would seem to suffer from persecution. Their presence is dangerous, because it means Fairytale might attack the Academy to get rid of them. Then, there's the fact that humans comitted genocide on multiple species that has likely left some Youkai sore. Plus, they'd have numbers and individual power over the human, so it'll be good fun for them to bully it anyway.
So, practicality is ambiguous, socially dangerous.