Are Ayakashi Dead creatures? Or some other manner of spirit? [Sabriel leans forward, curious.] Although this path seems visible to everyone here- there's even a sign.

[His next words give Sabriel pause. It's possible some other entity is responsible for this, but she also remembers the traps and protective spells set up around the royal graveyard.]

I'm familiar with the general idea, but there is another possibility- Instead of being actively maintained, this could be a spell, cast for some unknown purpose, and then left alone- it's possible that the one who originally cast it has since left, or is long dead.

But if this is the work of some sort of spirit, it would be best to banish or seal it, if it proves a threat.