Demon: Bishamonten
Requirements: DCM: Bishamonten | Demon Crystal: Bishamonten | Demon Card: Bishamonten | Visravas | Three-Bladed Vajra
Head towards Ueno and climb the spinning hill in the middle, reaching the pagoda. There will be two Gaian Priests there. One of them will mention something about trying to remember someone, and he'll ask you for all five Bishamonten-related items in sequence. Show him all five, and he'll keep the Visravas, and give you the Bishamonten Plugin: Guardian of the North in exchange for your help.
Death's Shadow