私の義理の妹は私に彼女を私のアパートで訓練させるように頼み、その見返りに彼女は私に彼女とセックスさせます

My sister-in-law wants to get in shape and since I have all the machines to train in my apartment, I leave her on the condition that she lets me fuck her and to my surprise she accepts with a smile on her face as if that was what she wanted in the end