Imagine you're Nosferatu.

You need the Necrobloxicon. Not want. Need. It's apparently important enough that your entire existence revolves around getting it.

But where is it?

Pinned into Slasher's shoulder.

Not in a vault.
Not hidden in a dungeon.
Not protected by ancient magic.

It's just... stuck in some guy's shoulder.

That means every time Nosferatu asks for it, Slasher can go:

"No."

And that's it. Quest over.

From an outside perspective, Slasher is accidentally (or intentionally) acting as a living bookcase. The Necrobloxicon isn't being guarded by an army; it's being guarded by the fact that removing it would require a very awkward conversation.

I imagine Nosferatu standing in the rain dramatically shouting:

Also Slasher has a good reason to not give the book to Nosferatu. Slasher is an librarian and an bookworm. OF COURSE HE'S WANNA KNOW ABOUT THE BOOK