A Sister's Secret/Threaten to tell your parents
Seeing your little sister get into serious trouble would be quite satisfying. However, it would be nowhere near as satisfying as cumming all over her chest or feeling her lips wrap around your cock. So clearly your only real option here is to use your new discovery as leverage to get what you want. This box will have to go back though, there’s no question about that. But you have a perfect plan.
You remove your aunt’s ring from the pile on your bed and hide it in your closet. That’s all you need...
···
“Hey Sarah, can I borrow a $20?” you ask the next morning when you see her walking by your room.
“Um... I’m 7, how would I have any money?” She responds, stopping in your doorway. She is just out of bed and has only taking the time to change out of her pull-up and into a pair of white and pink flowered panties.
“Because you’ve been stealing money from mom and dad,” you answer slyly, turning towards her. The sudden look of distress on her face is immensely satisfying.
“That’s a lie, I haven’t stolen any money,” She retorts, still determined to fight until she’s proven guilty.
“Than how do you explain that box of money I found under your bed?”
Sarah freezes, “I don’t know what you’re talking about.”
“Right, I bet you don’t know anything about Aunt Carol’s ring either. Didn’t they say it was worth a few thousand dollars?” You have her and she knows it. “I’m sure mom and dad wouldn’t be too happy hear about how I found it in your room.”
“Please don’t tell on me!” She starts to beg, looking steadily more naked and afraid wearing only her panties.