Playing as Japan again, united the country by the 1480's (not my best time, which I wasn't able to replicate with Uesugi in the last few games. I got something like 1455 for best time or something). Get ready to take Korea, have three provinces with fabricated claims, take the appropriate mission, make sure I've got enough boats... and then they ally Ming. Welp, not playing Ironman, so I figured I'd just see how it went. I send 30k troops over and a couple battles put an end to the Korean army. Then comes Ming with like a 30k doomstack against my ~25k. I manage to win defensively and their low morale causes them to retreat back into Ming territory.
I _really_ need reinforcements but I have no manpower left, so I recruit 8 mercenaries, load them up into my 40 navy stack and thankfully make it past a blockade to deposit them on the mainland. Some skirmishing happens, but eventually Ming returns with a 55k+ doomstack. I figure this is the end, it's 55k+ versus my ~25k. I manage to hold my ground and end up winning, by a lot. I took 6,600 casualties, they took around 16,000.
They'll be back, and I really need reinforcements because I got knocked down to 16k troops that'll have to face off against more doomstacks. I recruit more mercenaries, but Ming distributes it's 80-combined-total navy to blockade me. Even though those mercs are sucking up money, they contribute to how Ming feels about the war (comparative army sizes), so I don't disband them. My mainland army is by itself, holding up in Hwanghae while some smaller stacks take the peninsula. I get the provinces I cared about and then send all but one cap stack to reinforce my forward defense in Hwanghae. I have reinforced to around 23k when the Ming doomstack returns. It's roughly at 39k. I hoped that my defense worked again, and it did. In return for less than 4000 casualties, I inflict 15k. They are very demoralized, and I decide to chase them down and end them to ruin Ming's manpower while my single capstack sits and tries to take the rest of Korea.
I manage to Scooby Doo chase Ming's demoralized stack (while it constantly reinforces from new regiments it builds) when I realize that I have almost no hope of killing this thing if Ming just keeps throwing ridiculous amounts of troops at it. Korean patriots spawn back in my conquered territory, so I leave with 12k out of Ming to fight 8k rebels. I fear that I'm going to be squashed between those rebels and the growing doomstack I left behind (I lost vision of it when it got back to around 17k) when, just as my armies are leaving Ming territory, Manchu DoW's Ming and I see 20k of their troops head down behind me.
YES! Thank you Manchu! You're the best! I make it back to the Korean patriots, which were actually worse than any other force I fought and got my forces dangerously low. The doomstack finally makes it out of Ming and away from Manchu at around 20-25k or so. I have around 11k at this point with like 6 regiments of 0 troops. I disband them and I consolidate as much as is reasonable since I won't be getting any more troops, only reinforcements from manpower (consolidating is necessary for winning fights if you really have to win them). The only thing keeping me afloat, really, are those 8 merc regiments I was barely able to maneuver past the blockades because they reinforce by themselves. This fight was much more close to me losing, but I managed to win, and a Manchu 15k stack followed the Ming forces and was able to finish them off. I cap the rest of Korea while Ming is busy with Manchu. Manchu peaces out after capturing 3 territories by settling for ducats only. A 30k Ming stack is headed right towards my depleted forces when I cap the last Korean province and then settle for 3 provinces and some ducats.
Lots of luck, there. Ming will likely recover and be super scary, but I think I'll be able to get more of Korea or perhaps vassalize them if I can manage it.