I finally managed to pull off a Japanese historical victory! Even crazier: I did it without attacking America! (Though I certainly had the military/industrial capacity to do so if I wanted.)
I'm a little hesitant to claim that I found the meta for how Japan "ought" to be played, but I think I did. So here's how I pulled it off:
I settle Kyoto on spot, and Edo north of the river. I adopt Citizenship and Clergy. The Himeji Castle is my first priority, and I run artists in both cities, with walls and castles to further boost

. I settle the great artists in Kyoto. With the Himeji Castle constructed, I switch over to Vassalage and Tributaries. I gradually build up my military in Kyoto (redistribution + tributaries) in order to prepare for my invasion of the mainland.
With my 1st goal completed in 1481, I invade Korea, take Shenyang, and take Beijing, only stopping due to expansion stability limitations. As I enter the Renaissance era, I settle Nagaskai (Northwest of gold tile), Sapporo (North of Dye tile), and a couple of Manchurian cities. I wait until this era to settle because new cities built in this era receive a lot of core buildings. I adopt Meritocracy, Regulated Trade, and Isolationism. I choose Isolationism because Japan's unique ability will keep me more or less at tech parity with the West, and I want to begin building my specialist economy. As I get closer to the Industrial era, and my stability remains solid, I begin taking more Chinese cities. When America spawns, I put most of my

into him.
After I enter the Industrial era circa 1860, I conquer the rest of China, take the Philippines from barbarians, and adopt Democracy, Egalitarianism, Constitution, Free Enterprise, and Nationhood. Open borders with all countries (except America). I build myself up into a strong empire, taking the lead in score. I build several wonders: Statue of Liberty, Abbey Mills, Westminster Palace. I use a spy to sabotage American production of the Statue of Liberty, but unfortunately I didn't notice that he stole the Tsukiji Fish Market from me, otherwise I would've sabotaged that as well. With the Chinese cities growing as large as they tend to do, my expansion stability is over the limit, but I manage to keep myself from going Unstable with other modifiers. I initiate two golden ages from my great people.
As I enter the Global era circa 1920, I do one last civic change, adopting State Party and Secularism (and my empire name fittingly changes to Empire of Greater Japan). I invade Indochina, take Indonesia from the Dutch (starting WW2 in the process), and, thanks to Secularism, build the Forbidden Palace. At this point, with my expenses cut down to a bare minimum, I can pump my research up to 90%, and even 100% if I finance it with great merchants and selling technologies. With no number of cities maintenance, and a free specialist in every city, acquiring more cities is my strategy, and I conquer as many cities in the area as I can. I tried taking a couple of vassals (primarily for the

benefit) but they both ended up collapsing.
With as many specialists as I was running at this point, and due to State Party, my

count goes through the roof, eventually passing 1,000/turn. I put enough

into the tech leading civilizations to keep tabs on their research, but I ultimately end up putting them all into America. I achieve my research goals, while stealing the technologies that America researched first. The great spy from Psychology I use to infiltrate America as well. I keep this up through the Digital era, and on through until my victory in 1979. Like I said, I had the capabilities to seriously cripple, if not destroy, America, but I decided against it, as my expansion stability was kept over capacity almost the entire game. That, and I saw that I would end up winning if I kept doing what I was doing, and I didn't want to risk messing with that.
I attached my save game from the turn that I won my victory, if anybody is curious as to what my empire looked like.
One more thing. I noticed there's a fairly common bug as Japan (not sure if it affects any other civilizations) where another civilization, be it Korea, China, etc., will respawn from under you when you are only at Shaky stability. Since the Civilopedia states that this should only be possible at Unstable stability, I wouldn't feel any moral reservations about taking notes about how your cities are supposed to be the turn before they spawn, and using the world builder to correct matters when they do spawn in.
