My sister-in-law is five years younger than me and has a very sexy personality. She's cheerful, friendly, and works hard as a housewife. However, one day, I found her sexy lingerie among the laundry. Since our household had always been free of anything sexually suggestive, this discovery became a huge turn-on for me. I kept recalling that image every day and masturbated frequently. But then, by chance, I uncovered her secret, and after that, our relationship changed completely.