>sister and I used to fool around a lot during our teens
>eventually stopped due to mutual guilt/shame
>(plus a close call on almost getting caught)
>over the next several years our relationship pretty much goes back to normal
>neither of us ever bring up the sexual stuff we used to do
>it's almost like it never happened
>then she winds up accidentally pregnant
>she wants to keep it but her bf doesn't
>they break up over it
>sister comes to crash with me while she figures out wtf she's gonna do
>the pregnancy makes her super horny
>and I unexpectedly find it to be a huge turn on too, especially once her belly is showing
>we eventually end up fucking a bunch
>including lots of spicy roleplay where we both pretend like I'm the one who knocked her up but we've gotta hide it
>eventually she has the kid and moves back in with mom and dad to raise it
>zero sex between us since then, we're back to not talking about it