One of the greatest advantages of the internet is that you can reach niche audiences with very specialized information. It used to be that you had to go to large cities to find rare merchandise that might suit your very special needs or find magazines on the racks of bookstores that cater to your peculiar interests. I remember my cousin from Tokyo, an igo fan, complaining about the dearth of igo magazines at our local book stores. Today, the internet has given everybody everywhere the ability to find information on the most obscure hobbies and find like-minded souls. That is how I got to learn how to make netsuke in the rural area where I live. Thanks to this development, formerly unprofitable ventures can find the small number of consumers that can provide enough to make some sectors viable.
You can manufacture ultra-accurate miniature table saws specialized for making model ships and railroads, or prefabricated shell inlay material for luthiers (musical instrument makers) and build a sustainable business.
Writers too can benefit from this because, for example, if there is only a small demand for samurai and ninja fiction in the world, I could theoretically find my own niche in this area if I can come up with some quality product. There is an audience out there for books about sailing, or nautical adventures. There is an audience out there for stories about antique curators and wine tasters. Maybe there is a niche market for books about Australian vampires that breed zombie kangaroos. You never know.
The bottom line is, micro-audiences are real. Non-fiction writers are taking full advantage of it. I used to think that a community of pickup artists was a niche thing. Today you can find an audience of extreme misogynists, reverse misogynists, religious nut cases, cults, racists, victimhood pushers, end-timers, anti-vaxxers, conspiracy theorists of every hue and texture, and political extremists of an array of flavors all making good coin off their respective micro-audience echo chambers. Why can’t fiction writers do the same thing?
Books about how to write fiction used to be hard to find in the provinces. Today there are so many you can’t keep up with them. Writers are a small group of people. There are much more surfers than writers. Yet people are making a living off of this small audience. How about car enthusiasts? If you are knowledgeable about cars, you might find a niche market writing about people in suped-up cars. Of course Japan would have motorcycle literature. Yoshio Kataoka et al wrote about life with motorcycles (and a whole different biker culture from what you know in other coutries). We can go much more niche than that today. How about some bio-chem thrillers? Mermaid romances? Young android adventures? Dremel porn?
(Editing dilemma: Which is funnier, “Dremel porn” or “sapiosexual pornography”?)
Even before the internet, there were specialized magazines for some very niche interests. There is a magazine for enthusiasts for building wooden boats. And everything there is a magazine for, there is room for books. Even fiction books.
You have to focus on a small but passionate audience. How about existentialist soul quests for digital nomads? How about a Jurassic botanical park of giant venus fly traps for the vegan readership? Retrograde amnesia mysteries for mnemonists?
If you can find a passionate micro-audience, no matter how small, and provide a quality product, you can cultivate your own custom tailored market. That much is a given. It is just difficult to figure out what exactly might be out there.