As mentioned above, the story is written in simple present. The character, however, has an internal monologue about the past. Do I use simple past or past perfect?
You could use either, but if you are going to use simple past make sure the relative times of events are clear. Also, if this internal monologue is a direct dialogue from the subject (if you're using quotation marks), I'd use the simple past because the past setting that the story's taking place is the present in the subject's mind.