It is a part of unicorn physiology, I am assuming. I and others suffer similar conditions.

[Not that she's ungrateful for it. The ease of telekenisis makes up for the lack of hands.]

I would not use the term 'youkai people'. That is an impossibly broad term, and by no means are they all united. The closest translation of the term is 'demon', though much connotation is lost by doing so.