How many movies have Gou Koga and Kappei Yamaguchi collaborated on?

They have worked on 2 movies together! Their first movie together was One Piece: Clockwork Island Adventure (2001) while their highest rated movie together was One Piece Episode of Sabo: The Three Brothers' Bond - The Miraculous Reunion and the Inherited Will (2015). They have not worked together since One Piece Episode of Sabo: The Three Brothers' Bond - The Miraculous Reunion and the Inherited Will (2015).