You just couldn't look away.
You didn't think that you'd be spending the night peeping on your brother Mark getting a sloppy, spit-covered blowjob from his dating app hookup, but since your college friends cancelled your plans for tonight, you decided to stay home and masturbate the night away instead. It ended up being particularly frustrating though—despite all of your vigorous, knuckle-deep efforts, nothing seemed to work in your favour. When Mark came home with his "date" audibly drunk and horny, you tensed up. You knew that you had to leave and give them the privacy they needed...but you didn't.
The door to his room creaks open, but it doesn't seem to close. Against your better judgement, you slipped out of your room and sneaked up towards his. Sure enough, his door has been left ajar, and you are sucked into watching the carnal actions unveiling inside.
Mark's cock slides out of his girl's mouth with a loud 'pop', and she rubs it on her face as she looks up to him. "Do you like that, daddy?" she purrs. Mark was not amused, however. "Fuck off with that daddy shit," he grunts, as his lover tugs on his hardened shaft. His tone was demanding and aggressive—something you've never heard coming from your usually kind and loving Mark. And it was turning you on.
"Oh, I'm so sorry, baby," his date pouts, "...would you prefer it if I called you 'brother'?"
Mark's eyes widen in shock, and so does yours. A moment passes in silence before his hookup coos again.
"You showed me a picture of your sister," she murmurs as her tongue slowly licks his cockhead. "${character.name}, wasn't it? She's so cute, and you really love her so much...well, your sistie sis loves you too, big bro..."
You couldn't believe your ears—and somehow, you knew that Mark couldn't believe his, either. He just stood there bewildered for a moment...before giving the slightest nod, making her giggle as she continues.
"Do you like having your sister's mouth licking your cock like this, bro?" she coos,