I don't entirely know if this is the right board to put it, but a curious idea struck me and I believed it would be very homebrew as it would require quite a bit of work by a GM.
The Apocalypse; Inspired by the story of Onimusha: Warlords, Onimusha 2 and Onimusha 3: Demon Seige... The forces of the Shadowlands manage to either find a way around the Kaiu Wall or break through it after a period of relative peace where they build up their strength for one massive push into the southernmost part of the Crab lands.
Now, the monsters of the Shadowlands are on the surging tide and the families of the Crab have been pushed back to the edges of their lands in a far more desperate battle as a group of heroes muster the imperial forces and the standing armies of the remaining clans and attempt to push the shadowlands taint back to the breach.
Don't know if it would be a good idea, but it made me think both of horror tropes and even the mass battle tropes of Samurai Warriors as the players lead cohorts of soldiers against the forces of the shadowlands and try to at least hold key locations and strongholds to help push back the tide of monsters.