Write your characters however you want. If you want Mera to be trans or futa, go for it. But don't worry about the whole multiverse/dimension thing. This is erotica and making things overly complicated is a sure way to make readers alt-backarrow and not finish the story. And we have seen this play out over and over with the comic-based films over the last years. Too much alternate reality/dimensions/universes/timelines, that we couldn't keep track of it. And we lost interest.