found this on another site, just tried it out, and it worked!!
stripclubdj
Stage: Osaka Campaign
In Empire Mode, play the special stage "Osaka Campaign" and save your game.
OK here is exactly what i did.
Start battle of Sekigahara (1600)
Play on Novice
Change setting to MAX officers
Go to fief "Kai" and exchange Yukimura with okuni
Go to fief "Settus" and Place Yukimura there
Start the game by selecting the fief "Settus" which is controlled by
Hideyouri Toyotomi, and also now has Yukimura as a General.
That's it, Now i just put my defences to max, my troops to max and
keeps hitting proceed until the year 1614, Then I check to make sure
all my people have max troops. And when 1615 comes you should get a
prompt to participate in the battle of Osaka.
You can train your guys build up there weapons whatever you want to
do just defend the 2 feifs "flawless i tried this like 10 times with a
couple walkthroughs and this one worked first time.
P.S I stole this from xbox.com so please dont praise me
guess
i didnt see it here, eitehr way it def works. just set it up like that,
and just proceed. near like 1610 or so i had to defend a few times, but
beyond that i never attacked or joined in on any allies fights...