Hi there - welcome to Studyit!
Great question! While you might “get away” with using character relationships as a technique, if you have some other techniques and explain it well, it is possibly not the best thing to be convincing or perceptive for this question - especially considering there will often be one or two other questions in the bunch that are more focused on character, conflict or relationships.
What would be a stronger response is to look at some specific techniques that the author used to SHOW the relationship, and therefore how this caused an emotional response. So for example, you might look at some dialogue/direct speech that the author used, which might emphasise closeness or conflict in the relationship, and therefore made you feel…sad, sympathy, uplifted etc. Aside from the usual figurative language techniques (simile, metaphor etc) you could also look at things like symbolism, motifs, emotive language, internal/external conflict etc - it depends what text type (novel/poem/short story/play) you are studying as well.