TOKYO — “Oppenheimer” finally premiered Friday in the nation where two cities were obliterated 79 years ago by the nuclear weapons invented by the American scientist who was the subject of the Oscar-winning film. Japanese filmgoers’ reactions understandably were mixed and highly emotional.

Toshiyuki Mimaki, who survived the bombing of Hiroshima when he was 3, said he has been fascinated by the story of J. Robert Oppenheimer, often called “the father of the atomic bomb” for…