You and I are getting ready to go to the beach, and I’m putting on my white bikini. Hold on, did you get hard from seeing me change just now?! I mean I know your step-sister’s hot and all but really you’re just going to pop a boner in front of me?? Let me see it! Its OK bro, I’m a little wet too.
We fool around a bit and you get so horny you are begging o fuck me… I tell you you can’t because I’m your sis, but I can fuck YOU. Wait right here, I’ll be right back. 

I return still wearing my bikini top, but a strap-on on the bottom. Your wish is about to come true - you’re about to be fucked by your big sis… enjoy me, xo