Pain can be efficient or counterproductive depending on the individual. The threat or pain is usually more efficient than the pain itself. Your “let’s be pal” approach is not far from the KUBARK’s recommendations, but it is not incompatible with coercitive methods: On the contrary several of these consist in putting the interrogatee in a state where the interrogator is perceived as a reassuring presence.
I’m really into animation, so my favorite is The Greatest Living Show by Itoki Hana and Toby Fox. It’s a rather recent one, but my second favorite is a classic : Love Is All by Roger Glover and Ronny James Dio.