Short answers, pulled from the story.
The Soviet-Japanese Neutrality Pact was a non-aggression agreement between the Soviet Union and the Empire of Japan, signed on the 13th of April 1941. It came two years after the Soviet-Japanese Border War and let the two countries avoid fighting each other for most of World War II.
The Soviet-Japanese Neutrality Pact was signed in Moscow on the 13th of April 1941.
Japan's Foreign Minister Yosuke Matsuoka and Ambassador Yoshitsugu Tatekawa signed on behalf of Japan. Soviet Foreign Minister Vyacheslav Molotov signed on behalf of the Soviet Union.
The Soviet Union wanted to secure its eastern border and focus on the European theater of World War II after the Fall of France. Japan wanted to secure Manchukuo's northern border and improve its international standing while bogged down in its war against China.
The Soviet Union denounced the pact on the 5th of April 1945, citing Article Three's right of denunciation one year before the five-year term expired. Soviet forces then invaded Manchuria on the 9th of August 1945.
In the last campaign of World War II, Soviet forces took Manchukuo, Mengjiang in Inner Mongolia, and northern Korea. Japanese forces on the Asian mainland were unprepared and were overrun relatively quickly.