What! ? Seriously? My senior's slutty sex friend was my older sister! My older sister showed me a photo of my recently created sex friend! ? My sister, who grew up in a school with strict rules for elementary, junior high and high school, is extremely strict and shitty. To be honest, he's an annoying person who always keeps silly preaching to me. However, only after entering university was happy to be cheered on by the opposite sex, and before I knew it, I had become a slut. I'm shocked to learn about my sister's true nature. What's more, will the senior be having a threesome next time? He invited me to do that! Inside I want to make my reliable sister a mess one day...