I’m thinking of two films in which a bad guy (gangster, assassin) strikes up an odd kind of friendship with an unassertive law-abiding type, and by the end of the film the law-abider has manned up and found some kind of inner steel, largely because of the influence of the baddie. The films, both first-rate, are John McNaughton‘s Mad Dog and Glory (’93) and Michael Mann‘s Collateral (’04). There must be a few more. Would Delmer Davies3:10 to Yuma (’57) qualify?