From Wikipedia's article.

Gekokujō is a Japanese term for "overthrowing or surpassing one's superiors". It is variously translated as "the lower rules the higher" or "the low overcomes the high".

Gekokujō is a kind of "government from below" that is condoned; and a "government of men" is contrasted with a "government of laws."

Gekokujō became prevalent during the Sengoku period, starting with the Ōnin War when the power of the Muromachi Shogunate ended in factional strife and the burning of Kyoto. Without the imprimatur of the shogunate, provincial daimyo were vulnerable to being overthrown by forces both from without and within their domains. During this period vassals betrayed their lords and in their turn were in danger of overthrow from below. Clerics and peasants sometimes formed ikkō-ikki in rebellion against the daimyo and succeeded, for a time, in establishing independent realms.

How would you put that in place and justify it in Rokugan?

First of all, the emperor should be a kind of puppet similar to Gozoku Era, and clan internal strife and wars should be common, as well as inter clans skirmishes and castles conquests.

It helps to use the concept of vassal families, to add diversity with family names and adapt the scale of the campaign.

Take a large province split between two factions, each sworn to a family, vassal of a different clan, with regional ties and history. War between them deflates the scale of the conflict from an open war between two clans.

Then the family victorious gains a large piece of land and maybe can lobby for status, earning Great Family status. An ambitious daimyo can take advantage to wrestle power from other great families.

The mantis would earn Great Clan status by war, bonding minor families and conquering great clan holding.

Dunno, seems pretty L5R to me in principle after writing this. But Gekokujo allowed an ambitious Nobunaga to pave the way for Ieyasu and the atmosphere of war and treason typical of sengoku aren't really canon Rokugani.

So what twist would give that Gekokujo feeling?

In our homebrew Rokugan, we have a similar thing going on because the Emperor and his central authority is literally unchallengeable. Whatever the Imperials want, they get it. And this is the tricky part. Because the Emperor and his Imperials only really want five things: Security, Wealth, Wellbeing, Influence, and Piety for all in the Celestial Order. Emphasis is mine, it really stands for everyone equally, from the lowliest commoner/servant to the most powerful samurai/lord. As long as a lord rules in a way that his/her subjects are safe, prosperous, happy, influential, and pious, everything is alright as far as the Imperials concerned, in fact, they will offer considerable help to maintain the situation.

Problems start when a lord does not respect one or more of these five aspects, and/or even violates some of them. This isn't exactly hard to do because Influence is somewhat poorly defined while the Security/Wellbeing/Piety triangle is very hard to work with. If the lord starts failing, one or more of his/her subjects might consider rising up against him/her as they indirectly have the Emperor's blessing to do so. Samurai, in particular, tend to be itchy for removing bad lords because their rigid code of honor doesn't give them a lot of leeway for anything else.

The actual agenda of the rebels usually determines whether they can succeed or not. If their rebellion stands on shaky grounds, then the nearby lords will unite with their beleaguered fellow to crush the rebellion. If the rebellion is justified, then an Imperial decree for removing the lord from power at once might end the whole thing without an actual fight. There are also complications like a poorly conceived rebellion doing so well they can retroactively justify their actions or the fighting between the lords and the rebels doing so much damage the Imperials put down both .

There is also another important detail: our Rokugan is huge . The standard measurement of domain is the province, a 15 miles x 15 miles are ruled by a provincial/local daimyo. All Clans have 1500+ such provinces, with the largest one having a whopping 4005 provinces. Even a rebellion that spreads to dozens of provinces will be just a storm in a teacup, and it is fairly uncommon that a rebellion can engulf more than a single province. By the time Imperial/Clan authorities arrive to deal with the situation, a rebellion should be already over, and the eventual investigation will be just an afterword (and can spike a counter-rebellion too). Thus the potential rebels might not fear immediate consequences even if their cause is transparent, as long as they deem their chance of success good enough.

Lords and rebels alike must heed other circumstances too, like Family and prefecture (administrative unit above province ruled by a prefecture/regional daimyo, 9 provinces = 1 prefecture) authority intervening as they have better reaction times, Imperial authority shenanigans (Miya Heralds bringing news of the rebellion faster than usual, nearby Imperial Embassy that allows immediate reaction, other Imperial operations in effect in the general area, etc.), political landscape considerations (a rival lord might intentionally fester rebellion to weaken the province for a future invasion), and of course Honor (samurai might hold back for the time being because of Duty, hoping that they can reason with their lord - and commoners have little chance for a successful rebellion in this case).

Overall, this kind of "from below" rebellions are somewhat common, but rarely do more than some local excitement and are relatively quickly abolished by higher (usually Imperial) authority. Classic treachery also tends to avoid these affairs, this is more of a sort of "roadside justice" kind of deal. A good lord will most likely never suffer one, and even a bad lord can dodge the bullet as long as he/she has a certain "political panache".

That's easy. If the Scorpion are actually going to Coup instead of finding a way to wedge a puppeteer's hand up the Hantei's posterior, just wipe out his line. We can still have a Clan War, but combine it into a Sengoku Jidai type of event instead of just repeating the events of the old game with some new Window Dressing. Present a choice of Emperor from each Clan, and if the Canon is written so that Daigotsu would exist, throw him into the running while creating a Spider Clan of sorts early.

thing is I wasn't asking how to justify or reinvent a Clan War, not even thinking about an emperor of each clan...

Ï specifically asked about Gekokujo. How would you make it that a minor lord from the Daidoji could overthrow a major lord from the Doji for example, and then rise to a position where he could control the Emperor and his court.

Gekokujo needs the sanctity of the emperor to be unchallenged, but he needs to be a puppet and the real power lies within a military leader. And that leader may come from low extraction.

Best example of Gekokujo is how Oda Nobunaga managed by cunning and audacity to overthrow Imagawa Yoshimoto, and then grow in power to make his bid on controlling Kyoto (and thus the emperor)

So probably it would need to start with a big civil war, like the onin war.