randomly in the swimming pool of the neko village, on land behind the cloths changing shed, to the right of the pool. It only shows up as a sparkle, and doesn't have text saying you got it.
Also, I've got a post that lists where every Item I found is, the guide to side content and secrets, so check there if you have any questions, and if it can't answer it, reply to that post if you ever find the answer please!
