How many movies have Shōji Sakai and Tsuyoshi Koizumi collaborated on?

They have worked on 4 movies together! Their first movie together was Jukujo Soap: Tsukinuke Hassha (1998) while their highest rated movie together was Tenshi ga boku ni koi o shita (2002). They have not worked together since Tenshi ga boku ni koi o shita (2002).