After the fall of Berlin, the Russian army attacked the 750,000 or so strong Japanese army in Manchuria and crushed it. So, when Japan surrenders, the Russian army is still sitting in Manchuria. Considering how long the USSR occupied East Berlin, as well as the animosity left over from previous conflicts with Japan, it seems that the USSR could have kept some or all of the Manchurian territory. What kept the USSR from occupying Japanese territory? What effect did the Russian Army in Manchuria have on the eventual Japanese surrender?
Well they didn't. The Soviets occupied the southern half of Sakhalin Island and the Kuril Islands, which had been under Japanese control, and is still somewhat disputed today (though Japanese claims to Sakhalin and most of the Kurils are largely resolved).
Aside from that, keep in mind that the Chinese communists were around then, and were given captured Japanese weapons out of Manchuria. I would argue that thus the Soviets didn't really want to annex territory in East Asia, and preferred to have local groups take control and effectively rule as proxies (as North Korea and China did, if only for a while).