It started off as innocent flirting between you and your Sister. Slowly but surely things start to escalate; messaging all of the time, sending each other naughty pics. Eventually you suggest that the two of you might as well fuck. You think your well behaved Sister will decline, but to your suprise she's well up for it! You are now both addicted to sneaky risky sex, emptying your load inside of your naughty Sis every chance you get - even with your Mom and Dad in the same house! Your Sister is scared you might get her pregnant, so suggests you cum in her ass next time. You both agree that anal feels good but nothing beats that feeling of your bare cock inside of her pussy. The thought of potentially knocking up your own Sister turns you both on. One day, out of the blue your Sister texts you saying she is pregnant... what have you done!? You know it's fucked up but you're both addicted to fucking each other now, and her pregnancy certainly won't get in the way of your forbidden fucks.