If I have a character who is a very special chosen one, and it’s also a sci-fi story, how quickly could they master fighting from zero ability and not be too implausibly quick?
I have no clue.
We’re talking about science fiction. So, that suggests there’s technology available to characters that exceeds the real world.
It’s entirely possible to imagine technologies that would allow you to implant advanced training into someone in a matter of minutes. That’s not just martial arts, that’s any skill.
The first example of this that comes to mind is The Matrix (1999), though We Can Remember it for You Wholesale, by Phillip K. Dick, and Altered Carbon, by Richard K. Morgan, both play with the idea of implanting memories into new bodies.
The problem you’d run into with any skill which required muscle memory is implanting the muscle memory itself. That’s a consideration, but it is solvable. Rental sleeves (bodies) in Altered Carbon are prewired with reflex packages. The Matrix is a computer simulation, so issues with muscle memory are ignored there. It’s an issue, but it can be accounted for. Either through more invasive skill implantation, or possibly even some kind of further augmentations.
So, how long would your character need? I don’t know. It could be as simple as, “take this pill and count back from 100.” That’s the joy, and difficulty of science fiction.
If you’re going to this route, you need to consider how it would affect your world. If your characters live in a world where developing an entire new skill is easier than treating a headache, that’s going to seriously affect culture and society. It’s also worth considering that, “off the shelf skills,” may be somewhat uniform. So, if two people had both gained strategic skills from the same processes, they’re more likely to have similar strategic doctrines. Someone from a different background might be able to account for and exploit that. This also applies to distilled hand-to-hand packages, where someone familiar with the package could probably anticipate how users would behave, and get ahead of them.
So, let’s rip the guts out of the chosen one. I realize my perspective is a little ironic given I just cited The Matrix, but I’m not a fan of, “the chosen one has superpowers.” Or at least, I’m not a fan of, “the chosen one has superpowers because they’re the chosen one.”
Chosen ones aren’t automatically cliche, however, that is a real risk. The more inherently special and unique they are, the greater that risk becomes. Through no fault of your own, the phrase, “very special chosen one,” sets me on edge. It’s not the wording, it’s the concept.
One of my favorite, examples of a “chosen one,” is the player character from Fallout 2. The Chosen One was picked by a village elder to go out and save their village. That’s it. While the game allows the player to announce themselves as “The Chosen One,” like it’s their name, and the rest of the world basically laughs that off. Outside of their village, they’re just another wandering tribal.
I’m bringing this up, because if your character is designated as, “the chosen one,” by someone without any real power, that’s just a title. A sheltered, or egocentric, character may not even realize that being designated The Chosen One is basically meaningless. Much like Jake and Elwood in The Blues Brothers, just because you think you’re “on a mission from God,” doesn’t mean that anyone else cares.
When the character is designated as the chosen one by a higher power, things can get tricky. The idea of a divine champion has been done to death. It’s become cliche through overuse.
These kinds of empowered chosen ones present a real problem to their writer. If you’ve said, “this character is The Chosen One,” and even worse, “they’re destined do this thing,” it strips a lot of tension from your work. Your audience knows your chosen one will survive, and succeed, because they’re necessary to fulfill the prophecy, or whatever they were tasked with. There’s a lot of variations to keep this interesting, but it is a plot element that needs to be handled carefully, with consideration towards how it will functions in relation to the mountains of fiction that went before you.
I’m going to step back for a second and just say this: It’s impossible to be 100% original. The problem with chosen ones is that they’re going to derivative of other chosen ones from other stories. That’s fine. That’s not the problem. Creativity comes from how you use this plot concept. Being labeled as cliche (in this case) only means that you failed to come up with something that felt fresh. You took the same plot components that many others have handled, but didn’t managed to assemble it into something that felt compelling. When I’m talking about cliches, and saying, “this needs to be handled carefully,” that’s what I mean. You need to take the parts of a chosen one, and assemble it into something that fits into your story in a new or interesting way.
In the narrow example of this question, we have two parts. We have the chosen one, and we have rapid training in science fiction. Both of these have been covered before. However, there have been many more works dealing with chosen ones, while the list of works where characters gain advanced skills through unusual means is much shorter. Between the two, it will be easier to come up with an original work using the latter.
Mixing different pieces together to get a different perspective, or reworking how those pieces function, is how you get original and creative works. It’s just that’s going to be a lot harder with plot elements that have been done to death.
With that in mind, I have no idea how long it would take. I don’t know what rules apply to your chosen one. I don’t know what technology your setting has. Either one of these can set the answer for your story. That’s under your control. Ideally you want to follow those answers through. Even if it’s just that your protagonist can quickly gain skills, that’s going to have a massive, long term, effect on them.
It’s your story. Do something creative with it. Just because something’s at risk of being cliche doesn’t mean you can’t use it, it only means you need to be more creative.