Yokai are mythical creatures from Japanese mythology. They are incredibly diverse in appearances, powers, and origins.
Kitsune are humanoid spirits with fox features. Generally known to be tricksters, they can shape-shift into both animal and human forms and use those abilities to pull various practical pranks, both harmless and dangerous.
Spirits are neither humans nor monsters. They are simply souls who still wander the world. Most of them are invisible to a vast majority of creatures, and eventually fade away as their soul weakens. Once in a while, though, one will absorb the powers of the place they wander, and strengthen their link with the living world, giving them a somewhat physical appearance and the ability to interact with the world.
Being souls of the dead, spirits tend to have unsettling and even frightening appearances and voices.
Spirits cannot reproduce, even if they’re powerful enough to physically manifest.