The Human Vapor (1960)

The Human Vapor 1960 / ガス人間第一号 1960 / Gas Human No. 1 , Gasu Ningen dai Ichigo

The film tells the story of Mizuno, a librarian at a sanatorium (implicitly for cancer), who has been given the ability to become vapor after a scientist does an experiment on him. Mizuno uses this power to engage in criminal activities, robbing banks to give the money to his dancer girlfriend. Kenji Okamoto is the police inspector after them. (wiki)