The "step thing" is just a plain incest kink for the most part, with "step-<whatever>" existing just to fulfill legal requirements as some countries have banned incest porn without it. Silly loophole, everyone knows what it's meant to be but required nonetheless. I think OnlyFans has too required it be "step-<whatever>" smut, and not (fake) incest.
I think the step- was originally just to get around sites that forbid actual incest or stuff claiming to be incest. Pornhub is the best example. Not sure if it's still not allowed or if it just became a meme.
Can't remember step-sis but for incest in general, she did a video where she calls you Daddy, one where she calls herself Mommy, and another where you adopt a catgirl which is kinda similar. You can search mommy/daddy/adopt in any of the video archives to quickly find them.