How do you kill the Emperor in the Soviet mission Mt. Fuji? This is the mission where you have just a conscript and your ally has a bear.

this is the easy bit,

travel south then west before turret turns into a gun turret. wait at top of stairs till guards run off. then go south then east. you get mission update to create a diversion. blow up the drum then the coast is cclear to go back and kill the emperor.
its the next bit im stuck on! i get wiped beforwe i can build a base.

PP and defenses... dont build an army... i had a well defended base, and my ally was dead leaving me to destroy everything with my apoc army

That's the thing! You shouldn't build units in the beginning! Build a Crusher Crane as quickly as you can so that you can spam defenses. Once your defenses are in place, then focus on building units that will also be used to defend your base. I'd recommend building plenty of TwinBlades and Tesla Tanks. Once you reach the Emperor's Palace, Use the TwinBlades to destroy the Palace. The King Oni that emerges is tough to defeat if you don't mass units. Focus maximum firepower on the King Oni and it should fall in no time.

When I got my base I just spammed bazooka guys and infantry for a bit then got anti air up.

Trust air units are so annoying in this mission.

build your defences up fast, make plenty of them, then queue up about 20 Apocalypses and some bullfrogs, then go north into a small empty area surrounded by walls and put your Apocs into M/Harpoon mode, you will see why, then continue from there