How many movies have Masato Kai and Takeshi Okubo collaborated on?

They have worked on 2 movies together! Their first movie together was Kyotaro Nishimura's Travel Mystery - Soya Honsen Murder Incident (2001) and was their highest rated movie together. They have not worked together since Kyotaro Nishimura Travel Mystery 68: Disappearing Woman in Yamagata (2017).