Forbidden sisterly love at the distance of an excited penis

Everyone should have their personal space, but how can you talk about that when you sleep in the same bed with your stepsister... and she sleeps naked. It's hard enough to deal with a morning boner, but then there's your sister's beautiful big ass right there, beckoning you, hinting at dirty incest. Yes, maybe your sister will play along when she sees her brother with a boner in his hand and staring at her ass, but only until that boner ends up in her pussy.