The library seems to have been built overnight. It's not very large, a little brick building tucked behind a house and covered by a curtain of ivy, and the only indication that it even is a library is the sign, which is also quite small. Perhaps it was here before, and you simply overlooked it until now, although you have a strange feeling that this is not the case.
It's probably not safe to go into mysteriously appearing buildings, but you do anyway. It's only a library. What could it do to you?
Inside, the library is cool and dark; what windows there are have ivy growing over them. There seems to be only one large room, lined with shelves and with a few chairs gathered awkwardly in the corner. There's one lamp, on the circulation desk, and it's turned off. Behind the desk is a large newspaper, which after a few seconds is lowered to reveal a Yonyuu wearing what must be the tiniest glasses in the world.
He meets your eyes for the briefest of moments before looking back down at the paper spread before him. "Is there something I can help you with? A magical artifact you wanted me to identify, or...I am rather busy, you understand."
He certainly doesn't look very busy to you.
"Mm, wait. I know why you're here." He reaches under the desk and presses something that clicks loudly, then pulls out a drawer and sets it on the desk. Inside is a line of little plastic cards, separated by plastic dividers. As you watch another card pops into existence.
"The catalog," he says, and the corner of his mouth twitches. "People who know people who know other people. One of the stranger devices I've been given. Eventually I imagine it won't fit in the drawer anymore, though that day is a ways off." He pushes the drawer toward you. "Go on. Everyone comes here to look at it, and almost everyone finds who they're looking for. Someone they know, someone they ought to know, someone who can solve a problem they've been worrying about or one they didn't even know they had. It's some sort of powerful magic. We've never been able to determine what kind."
You take the drawer with you to the table in the corner, and begin flicking through the cards. Somehow you wouldn't have expected magic to work in plastic. Most of the cards don't have contact information on them, but there are a few; people the catalog thinks you need to contact, maybe. If you believe what the Yonyuu says. It would be perfectly reasonable not to.