You look over your shoulder in horror as you see that Abigail has pulled out her shemale cock and is stroking it to full hardness. You know what you're in for and this time, with your dad and stepmom out of town, there's nobody to stop it. She grins at you as if reading your mind before effortlessly rolling you to your back and yanking your sleep pants off.
"No escaping, little stepbro," she giggles, grabbing your legs and yanking them upward so that your hips are elevated and the rest of you is helpless to get away, "Mama says we're supposed to love each other and I got lots of love for you. I'm gonna love you so much that by the end of the week you won't have a choice but to love me back!"
With that, Abigail shoves her shemale cock into your ass and squats to trap your legs and basically fuck you standing up. This isn't the first time Abigail has done this sort of thing to you. The first had been the night of your birthday when you reached the "age of consent" (not that consent has anything to do with what's happening now). Abigail had come into your room and told you that your stepmom had told her you and she needed to learn to love each other the right way, after which she'd tackled you in your bed, pinned you down, and showed you what she meant. From then on, she'd force herself on you whenever she could in one way or another. It'd typically be a quickie in secret since, while your stepmom obviously knows what's happening, for some reason they want to keep it a secret from your oblivious dad. Even while he's around, however, Abigail has taken to forcing "affection" on you around your dad and stepmom and even in public, hugging you from behind while rubbing her cock bulge against your butt, forcing sloppy french kisses on you in public places, making you give her full-body hugs while whispering what she's going to do to you next time you're alone with her.
"Oh fuck yeah!" Abigail moans as she continues to plow your butthole, now taking hold of your decently-sized cock and jerking it to an embarrassingly full erection, "it feels so good! I could do you night and day. You starting to love me yet?"
That's the most frustrating part of this. Despite the fact that your stepsister is forcing herself on you, she's not doing it out of sadistic cruelty or even stepsibling meanness. Your stepmom has her completely convinced that siblings are supposed to express their love sexually and by repeatedly forcing herself on you, she can make you love her back. You can actually feel for her in a way. All she wants is to be loved, it's not entirely her fault that she has such a skewed view of what that actually means.
As she adjusts her position so that she's essentially lying on top of you and putting all her weight into her thrusts, you begin to wonder (not for the first time) what it might be like just to give in, to let her "love" you and even give her a bit of "love" in return. Granted you don't want to let your stepmom win and certainly don't want to enforce the idea to Abigail that this is the way to go about getting loved, but on the other hand if you convince her and your stepmom that they're successful, maybe they'll be satisfied with it. Besides, if you try to comply, maybe you can convince Abigail to "love" you a little more gently. Might be worth a shot.