Good news! The cover doesn't read "Stepfather", it literally reads, "Papa" (パパ). Even in Japan a young woman will sometimes address her father casually as papa. That word is universal. I haven't seen this one but It's probably translated with the "step" due to the recent rise in power of Japan's private ethics companies, that try to guide porn producers away from themes they deem morally intolerable; or just the translator adhering to a western moral standard that draws the line at the depiction of actual blood-relative incest. Many of the JAV you see on European or North Americans streaming sites with the words, "step sister" or "step mother" in their titles aren't actually "step" anything. It's just illegal to depict blood relative incest in western porn. It's not illegal in Japan but those ethics companies are trying to steer the industry away from so many incest, chikan, r*** and sexual harassment themed productions.
Anyway, now that you know the truth about this video, wank away anew, comrade. Wank away!