How many movies have Hachirō Kai and Shin'ichi Arai collaborated on?

They have worked on 7 movies together! Their first movie together was Uno Koichiro no Shûdôin Fuzoku Joshi-ryô (1981) while their highest rated movie together was Horny Working Girl: From 5 to 9 (1982). They have not worked together since Top Stripper (1982). They are most known for their drama films together.