Considering I wrote 7 sequels (and 2 prequels) to the Scarlet Knight series, 2 sequels (and a spinoff) to the Chances Are series, and 2 sequels (and a collection of short stories and a spinoff) for the Girl Power series it's kind of weird that I've only written four direct sequels since 2014. Those are both for Eric Filler series Gender Swap Challenge and Gender Swap Detective. Otherwise the "sequels" are unrelated stories.
Once or twice someone has asked if there's a sequel for a particular story and no there isn't. The thing about those gender swap stories is there's usually no point for a sequel. Because unless you change the main character into a man again (like in Last Chance) you can't really do a gender swap again. So for those sequels I did write it's the character changing into different kinds of women. Like in the Gender Swap Challenge it was the main character changing from a stoner guy to a bimbo, then into a sultan's plaything, and then a virgin schoolgirl. Or in the Gender Swap Detective stories first the hard-boiled detective turns into a beautiful woman, then an exotic dancer, and then a little girl. So really that makes those ones kind of hard to write direct sequels for them.
And storywise there's usually no reason to do a sequel for most of the gender swap stories. The character usually lives happily ever after or ends up unhappily ever after, but either way it's over one way or another. So in my mind there's not any unfinished business left behind.
Someone said about the novella From Warrior King to Peasant Girl: it ended when it was just getting started. And I'm like, "What the fuck you talking about?" I mean the King Arthur-ish character had become a little girl, grown up again, discovered she had witch powers, overthrew the bad guy, and retaken her kingdom. What the hell else was there to do? I guess unite the whole kingdom but who cares about that? I mean she has witch powers and a magic sword so it's not like that's going to be too hard. I really don't know how you could say it was just getting starting, but people are annoying.
I have a couple of ideas for gender swap series. First was the superhero-themed one Secret Origins and I have some vague ideas for a sequel. Then there's the Transformers-themed one Only Human where I'm thinking of having bad guys adopt human forms in a sequel. I also have an idea called Gender Swap Therapy where a shrink would be a recurring character who uses gender swapping/age regression to cure his/her patients. And another inspired by Quantum Leap would have a scientist "leap" back in time as various female characters. But those are just in the drawing board stage.
As for non-gender swap stories I just really haven't come up with any solid ideas. Mostly because no one buys the first book hardly so there doesn't seem to be any reason to waste time with a second or third one. With the Scarlet Knight, Chances Are, and Girl Power series I had ideas for sequels as I was writing the first one but Justice for All (The Outcast #1--and only?) or Army of the Damned (Sky Ghost #1--and only?) I didn't really think of anything solid at the time and I haven't spent a lot of time thinking about them. Someone said about Justice for All (The Outcast #1--and only?) that "You can't leave it like that" and I disagree. I have absolutely no idea why I can't leave it like that. The main character is alive and going back to school in the town where her boyfriend lives. The Kingpin-ish bad guy is still out there, but so what? It's not like it ended on a cliffhanger.
Lately, maybe because I watched a couple of Mad Max movies I was thinking of something similar to do for a Sky Ghost sequel. The idea would be the good guys are starting to run low on gas and so ace pilot Hunter Hawking is out looking for some when he stumbles across an oil tanker that's run aground but still has plenty of oil on board just waiting to be plucked. So they'd have to clear the ship of zombies and get the oil off it (or maybe get the ship working) and then try to get it back to their home in Salt Lake City while some other groups try to steal the oil from them. Maybe I'll do that or maybe not. Since it has zombies I just don't want to be like The Walking Dead and just have it be they find a group of survivors who are good/evil and then mayhem ensues.
Long ago someone suggested I write a sequel to Where You Belong and I'm like, "I have no idea what that would be about." I mean I was using the cradle-to-not-quite-grave John Irving formula, so what would there be to do in a sequel? If it were going to cover another 35 years it'd be going until like 2044 so then it'd be science fiction instead of literary fiction. I guess that's why Irving doesn't write sequels. And more to the point I don't think I'm ready to write about Frost Devereaux in his 40s, 50s, 60s, 70s because I haven't lived that yet. Maybe in another 30 years...
But I don't know. Maybe if someone has a sequel idea for another story they can send it to me.