With the new season out, I was sort of thinking about how a lot of the strong parts of the series have to do with the people on the far side of the gate attempting to deal with something that they are only just starting to realize is an outside context problem. Like how the emperor is continuing to use the gate in a push for centralization, to wipe out the armies of his vassals and sweep away the senate as a political body with teeth, not actually recognizing the actual danger because he still thinks he's playing by the old rules.
That's really neat when you think about it actually. In another reality he could have gone down in history as his people's Louis XIV, regarded as a centralizer who broke the backs of corrupt nobles to install more modern institutions in their place. You can have all of these people acting like actual people with agendas and intelligence, all clashing with the fact that they are up against a force that can utterly steamroll them.
I've also sort of batted about the idea that for something like this, a big military confrontation should be seen of as a failure state the protagonists should be desperately trying to prevent. Why? Because as long as they can keep it down to a plausibly deniable 'policing action' Japan can remain in primary control of the gate and only have to invite in token international observers. If they actually get into any sort of serious slugging fest, even if they win that means that the international community is going to step in and Japan gets demoted from sole controller of the gate to senior partner or even secondary partner. If the US, Russia, and China want in, there is nothing that Japan can do to really stop them, the international pressure that can applied is simply too great. So long as everything remains at a dull roar and the most they have to do is occasionally defend a village or town from bandits Japan can act more or less in its own interests without losing military control to America/the UN and can thus set down the deepest economic ties for the long run.
This also lets you excise the Diet bit about the gross and predictable "left wing career politician tries to micromanage the military and they just don't know what it's like down there" trope. Make them getting summoned back to the Diet be more about how "No, seriously, we have this under control we don't need backup" and at least then the other nation's involvement can go down to them trying to get a more accurate picture of what is going on, and them being less stupid about it by actually sending in hit squads of their own people. Again, all America has to do is to make sure that the people from the other side of the gate are extended an invitation to the UN in New York and they get what they want, no need for violence.
Also, by having Japan not want this to go to all out war, you can get scenes with the ambassadors basically eventually breaking it down into terms the people from the empire understand by saying "Look, we don't want this to be an actual war because then our liege nation steps in and we don't want that." The relationship between the US and Japan is obviously more complex and subtle than that, but it gets across the concept and would produce a suitably horrified reaction from the generals and senators they would be telling it to. Could also be useful for telling them "Look, don't start shit, it ended badly for us"
But then again none of that would feed into the ultranationalism and JAPAN STRONK of the author, so yeah, unlikely in the least.
