Answer:
persuasive letter
Explanation:
Your intent, in this case, is to change someone else's opinion. To make them think like you, or like you want them to think. In this case, you don't need a narrative, and a story, about whatever or whoever, by itself won't do either. Your goal is to persuade them: to "cause (someone) to do something through reasoning or argument," therefore, you need a persuasive letter.
