[This was a custom request] You're in your room enjoying your guiltiest pleasure - k9 porn on the internet - when your older sister suddenly wanders in. You slam your laptop lid shut in a hurry and she notices your panic. She begins to tease you, knowing that she's walked in on you wanking, and wants to see what you were watching. She tells you that she won't judge you (no matter what it is) and just wants to see. You're hesitant but you explain to her that you were watching doggy porn. At first she's confused and thinks you mean them breeding with each other and is weirded out by your strange kink but, when you explain that you mean doggies and girls, she is still taken aback but slightly more intrigued. At first she pretends she's not at all interested but soon asks to take a peek. When she sees the footage on your laptop screen you notice her becoming visibly aroused. She starts to touch her breasts and pussy through her clothes. That's when you get an idea. You get up and lead the k9 upstairs into your bedroom and to your sister. She refuses to do anything with the beast and explains that she was simply intrigued by the porn and that's it but the doggy starts to sniff your sister between her legs with his nose and you tell her that you think he wants to do it too. She tells you no again and again, explaining that she's ovulating and doesn't want to accidentally get pregnant with doggy cum, but eventually she can't hold back her desires and pulls her shorts across to let him lick her pussy. She loves the feel of his huge wet tongue on her cunt and quickly shudders to an intense orgasm. She pulls her shorts back up and tells you that she's had fun but that's it now. She definitely doesn't want to try what the girls were doing in the clips you watched together because she's too worried about accidentally being bred by the beast. While she's talking, she notices the k9 wandering around the room with his big cock bobbing around between his legs. She looses her train of thought watching him and you know that your sister is desperate for doggy cock inside her pussy. You tell her to bend over on the bed like the girls in the videos and guide his cock inside her - you can't help but to grab a handful of your sister's cunt while doing so. The k9 fucks her harder and deeper that she's ever been fucked before and she screams with pleasure, explaining that she's never felt anything like this before. You even begin to film her and she doesn't care - she's loving the doggy cock inside her way too much. She continues to remind you that he mustn't cum inside her though because she's much too fertile but you glance at her cunt and realise that it's too late for that. He's knotted her and is already pumping his seed inside her guts. You explain to her what has happened and she's shocked and upset... but as soon as she realises that she can feel his spurts inside her she becomes too turned on to stop it from happening. She begins encouraging the beast to shoot his load inside her belly - impregnate her with his pups and fertilize her unprotected eggs with doggy cum. When he eventually finishes and pulls out, gallons of cum leaks down between her thighs. You've turned your sister into a slut for k9 cock.