I haven't read the Otosan Uchi boxed set yet, which apparently contains information on running the Coup. When I do get my hands on that, the information here might change. Or it might not. We just...don't know. Anyway, here's how that wacky Shoju got that mean 'ole Hantei to play all dead.
Coup-3 years (summer): Tensions between the Crab and the rest
of the Empire reach an all-time high. Kisada practically cuts the Crab
off from the rest of the Empire. In my campaign, the problems really started
when the Imperial Legion under the command of Otomo Yasho didn't help defeat
the Shadowlands Incursion, but any triggering event will do.
The Scorpion begin making secret overtures to the
Crab, mainly through the Yasuki and Kuni. The Kuni have always...tolerated..the
Yogo, and the Bayushi merchants were willing to trade with the Yasuki despite
Kisada's decree of Crab isolationism.
Coup-2 years (autumn): Shoju discovers that Hantei the 38th will
be the doom of Rokugan. In my game, this happened when one of the seals
on the Black Scrolls was cracked. The visions this produced, in concert
with various prophecies of Uikku and Scorpion secret records, convinced
Shoju that the Emperor must die.
He immediately began secret talks with Kisada, offering
the support of the Scorpion Clan to Kisada. While the Great Bear was initially
suspicious, Shoju offered him essentially a risk-free proposal. The Scorpion
would do all the dirty work - take Otosan Uchi, kill the Emperor etc. All
the Crab would have to do would be save the Scorpion.
Around this time, the Shadowlands grew very quiet.
Hiruma scouts reported that there wasn't a single goblin within three hours
of the Wall, and no Oni or undead could be found. This freed up the bulk
of the Crab army for...war games.
Coup-22 months (winter): Up until now, the Coup was known only
to a handful - Shoju, Kachiko, Kisada, and their most trusted advisors.
Now, Shoju begins issuing commands to the Scorpion daimyo. He orders them
to prepare their troops for city fighting and siege warfare. He also asks
for an extra tithe of their treasuries, to fund various secret projects.
The letters detailing these orders were encrypted, and the method for decrypting
the letters was taught only to the daimyo themselves, at Winter Court.
For a thousand years, the Scorpion have guarded
a secret - there is a hidden pass in the mountains, which leads from Scorpion
lands to the lands near Otosan Uchi. The pass is difficult and treacherous,
useless for any more than a handful of men. Now, with the extra money,
the Scorpion begin building a new road in the pass, a road suitable for
bringing hundreds of thousands of troops through the mountains and into
the imperial lands. The name of this hidden path is the Chrysanthemum Road.
Coup-18 months (spring): To hide the construction of the Road, the Scorpion begin several cover projects - the building of a new port city and roads in the south. Building materials are secretly diverted to the Chrysanthemum Road. Meanwhile, Shoju draws up plans for restructuring the Scorpion armies, from a loose feudal arrangement into a well-trained, cohesive standing army mirroring the Imperial Legion. Each daimyo is ordered to prepare a hiding place for his family and vassals, in the event of disaster. Shoju begins experimenting with cannons and firearms, to be sure of having a final weapon.
Coup-1 year (autumn): The Scorpion launch a massive infiltration
campaign, designed to identify the key commanders in the Imperial Legions
and Akodo Guards. Around this time, Hatsuko (Toturi's geisha) is subverted.
The Scorpion also form the Ghost Samurai units -
Shoju issues cheap swords and armour to ashigaru. These Ghost units allow
him to move elite Scorpion samurai into his standing army without the other
clans noticing.
Coup-9 months (winter): At the start of the winter court, a Scorpion plot involving gaijin causes the Lion/Crane feud to explode. The Lion blame the Crane for the attack on the Imperial Commander, Seppun Ishikawa. During the court season, Scorpion diplomats turn the Clans against each other. By spring, the Lion and Crane are at war.
Coup-six months (spring): The road is almost ready. Shoju pulls
the bulk of the Scorpion samurai into his army. The Scorpion provinces
are reduced to a skeleton guard. Spies and courtiers ensure the Lion/Crane
war continues.
The Scorpion shinobi-masters gather the Shadows.
(See Reworking the Shadow).
Coup-two weeks (autumn): The Scorpion army marches from Kyuden
Bayushi. A massive Crab army musters deep in Hida lands. A much smaller
Scorpion army is sent via Beiden Pass.
The Ninja flit ahead of the Scorpion army.
Coup-one week (autumn): Junzo uses his magic to confirm that the Crab are ready, and that the Imperial Legions are in their expected positions. The signal goes out.
Coup-six days (autumn): Ninja assassins are despatched to remove the key commanders identified last year.
Coup -five days (autumn): The Scorpion emerge from the mountains, and race for the capital. Their scouts are accompanied by small elite units, and ensure as little news as possible reaches the Imperial City.
Coup-four days (autumn): Assassins kill their targets. Toturi should have been killed, but Hatsuko is weak and merely drugs him. The Legions are left leaderless, and crumble before the Scorpion assault. The Scorpion approach the capital.
Coup-three days (autumn): The Scorpion surround the Imperial City on three sides. Ninja infiltrators go through the sewers.
Coup-two days (autumn): One of the Walls falls to the Scorpion. The fighting goes to the city streets and buildings.
Coup-one day (autumn): The Emperor is trapped within the Imperial Palace.
Coup!: The doors of the Palace are blown open with cannon. Shoju kills the Emperor and takes the throne. He orders the city sealed. The trapped Otomo and other Imperial bureaucrats are slaughtered.
Coup+two days (autumn): The City is secured, a few hours before the Crane army arrives.
Coup+four days (autumn): The bulk of the Crane army arrives, as does a large contingent of the Phoenix army. The Unicorn scouts arrive.
Coup+seven days (autumn): The Lion arrive, and lay siege to the city, as do the Unicorn. Crane/Lion hostilities delay the siege. Rumours state that the Emperor is being held hostage within the city, and the siege is stopped until the assembled armies can be sure that the Emperor will not be harmed by their actions.
Around here, events in the Chrysanthemum Road diverged from Shoju's plan, and canon L5R.
Coup+nine days (autumn): Shoju sues for peace. This is seen as a delaying tactic by the Lion. Hoturi sends messengers to fetch the Emerald Champion (who has also been attacked by assassins).
Coup+ten days (autumn): The Scorpion army sent via Beiden Pass arrives, and draws away a portion of the Unicorn. The Scorpions retreat away from Otosan Uchi.
Coup+twelve days (autumn): Matsu Tsuko orders the Lion to attack the Imperial City and kill the Great Traitor. The Scorpion hold the walls.
Coup+two weeks (autumn): The Crab arrive.