Oyayubi Sagashi

There is a metropolitan legend which is about a girl assaulted and cut in pieces by mysterious assassins in a building now abandoned. The legend continues with telling that a finger of that girl has never been found, and whoever will find it can ask for a wish, which will be granted.
A group of guys, for fun, choose to try going at that place and look for the finger, but one of them disappears.
Seven years passed since that tragic event, and the guys finally decide to look for their friend...