How many movies have Akira Toriyama and Takao Koyama collaborated on?

They have worked on 13 movies together! Their first movie together was Dragon Ball Z: The World's Strongest (1990) while their highest rated movie together was Dragon Ball Z: Fusion Reborn (1995). They have not worked together since Dragon Ball GT: A Hero's Legacy (1997). They are most known for their action films together.