xxxHOLiC: Manatsu no Yoru no Yume

Invited to a wealthy client's mansion, time-traveling witch Yuko and her companions arrive to find a group of collectors assembled to participate in a mysterious auction. And the mystery only deepens when the collectors go missing one by one. As more guests disappear and strange occurrences abound, Yuko and her friends realize they must solve the mystery before they vanish as well.