Very spoopy! I liked it a lot.
My favourite part about the gameplay is the ghost's movement. It appears and then aims at your position, but doesn't actually chase/home into you. It lends to an interesting strategy: when the ghost appears, stay still, and then run in a different direction from where it aims at you. It's a good way of dodging it while also conserving your stamina.
It took me a while to realise that the pink arrow that appears around Koa actually points to nearby books, mostly because it disappears and reappears pretty often. Maybe making it bigger and/or the same colour as the books would help?
Good job on the game overall! Your team nailed the spookiness.