PARATHD-4258 My friend's sister is so cute and has so many gaps that I think I could do it (6)

But there's just one problem... Rina is my friend's younger sister. ◆At first, I was reserved around my friend, but I can't resist any longer. ●Rina is so carefree and defenseless that I invite her in for a physical relationship! ? I'll have sex with her when my friend isn't looking...