The detail that the most contribute to the troubled tone of this excerpt is: "I don't understand what my brother means when he says this. I wish I understood exactly what my brother wants me to be."
This detail highlights the narrator's confusion and lack of comprehension regarding her brother's desires and ideals. The use of "don't understand" and "wish I understood" suggests a sense of unease or concern about the divide between the narrator and her brother's perspectives. It conveys a troubled tone as the narrator grapples with her brother's thoughts and desires.