It almost did.
The Keian "Uprising" was really a coup attempt plotted by one Yui-No Shosetsu. Sometimes called "the Japanese Guy Fawkes", Shosetsu was really more like a Japanese James Bond villain. T
he son of a humble dyer, by the 1640s he had built one of the country's largest business empires around the manufacture and sale of high-quality armor and weapons. Meanwhile, in the shadows, he was organizing an army of masterless samurai, _ronin_. The Tokugawa Shogunate was pushing more and more samurai into ronin status, while at the same time clamping down on traditional ronin positions such as mercenary and bodyguard. The result was a large group of disaffected men with advanced weapons training. Shosetsu carefully recruited hundreds of them into an elite secret corps of killers, utterly loyal to him personally.
The plan of the coup was brutally simple: Shosetsu intended to use gunpowder barrels to set fires all over Edo. The resulting inferno would destroy the capital. (This was not speculative. Edo was all wood and paper construction, and would in fact be completely destroyed by fire just six years later.) More to the point, Shosetsu knew the government's emergency plans in the event of a major fire or other disaster. Most of the castle guard would be spread out across the capital keeping order, while the high council of the bakufu -- all the top officials of the Shogunate -- would gather in one location, partly for safety and partly for coordination. Shosetsu could, with a single attack, bag the entire top echelon of the government at once -- like a terrorist catching the President and the whole Cabinet in a single room.
Better yet, the Shogunate was, for the first time, under a regency; the previous Shogun had died in middle age, and his son was just ten years old. The Regency had been sworn in just a few weeks earlier, and its grip on power was not yet secure. So, it was not completely ridiculous for Shosetsu to think that he could take over the government. If he could eliminate the Regents, he then need only get an Imperial rescript appointing him guardian of the heir. The young Shogun could then be dealt with a few years down the line... this was, after all, exactly what Tokugawa Ieyasu, founder of the Shogunate, had done with young Hideyori forty years earlier.
Alas for Shosetsu, his right-hand man caught a fever and, in a delirium, babbled details of the plot. The bakufu's secret police caught wind, and all was lost. Shosetsu ended by committing seppuku, and his ronin were massacred in a Spartacus-style bloodbath of public crucifixion and torture.
But it was a damn'd close thing. So [handwave], no fever. The plot goes off, the fires are set, and Shosetsu takes out the bakufu. Within days, he's the master of Japan.
On one hand, I suspect he'd get away with it, at least in the short run. The Tokugawa Shoguns had spent the last fifty years relentlessly centralizing. The daimyo, the local lords, were increasingly neutered by a combination of a hostage system (they had to spend part of each year in the capital, with their families) and the growing power of a centralized Imperial bureaucracy. So, if Shosetsu could get firmly settled in the cockpit, it wouldn't be easy to get him out.
On the other hand, there'd be problems in the long run. While there was precedent for a peasant seizing supreme power -- Hideyoshi had done it seventy years earlier -- that was a rougher time. And even Hideyoshi failed to found a dynasty; his son and heir Hideyori was supplanted by Tokugawa Ieyasu. So, I suspect that this leads Japan into (at least) another generation of civil war. This is probably a bad thing for Japan in both the medium and the long term; OTL, Japan's 19th century modernization was firmly grounded in the long peace of the Tokugawas, with its concomitant political consolidation and economic growth. A Japan that has to hit "restart" in the late 1600s seems likely to be a poorer and weaker Japan in the long run.
Thoughts?
Doug M.