Convince

As you soothe your sore testes you come up with an idea that can save your balls...at least for today

"Sis wait!" you say right before she winds up another kick

"If we work together, you watch my back and I watch yours, both of us can come out of this relatively unscathed."

She stomps her foot down on your balls and the pressure sends a world of pain to your lower abdomen

"Please!" you say in a strained voice "If you team up with me then I'll let you bust my balls whenever and wherever you want after today!"

You finally feel her lighten up on your poor nuts

"Now that sounds like a deal" you hear her say