How many movies have Kenichi Ishimaru and Koichi Yamadera collaborated on?

They have worked on 1 movie together! Their first movie together was Ranma ½: The Movie — The Battle of Nekonron: The Fight to Break the Rules! (1991) and was their highest rated movie together. They have not worked together since Ranma ½: The Movie — The Battle of Nekonron: The Fight to Break the Rules! (1991).