From 1967 to 1970 he worked as the cameraman of the theatrical group Tenjō Sajiki, under Shūji Terayama.
Two years later, he left the magazine in order to pursue his own career as a photographer, and he became close friends with Shōmei Tōmatsu, Shūji Terayama, and Daidō Moriyama.
Mikami also acted in cinema and is notable for collaborations with Shūji Terayama and his avant-garde theater Tenjō Sajiki.