How many movies have Ken Ootsuka and Naoko Yamamoto collaborated on?

They have worked on 2 movies together! Their first movie together was Slayers Return (1996) while their highest rated movie together was Fullmetal Alchemist the Movie: Conqueror of Shamballa (2005). They have not worked together since Fullmetal Alchemist the Movie: Conqueror of Shamballa (2005).