Reimu previously resided at the Hakurei Shrine and also maintained the Great Hakurei Barrier before its collapse. After the collapse of said barrier, Reimu later decided to get involved in World Affairs.
The first affairs she got involved in was the Chinese Civil War and the Korean War, aiding both the Republic of China and South Korea respectively. In the Third Russian-Japanese War, she, along with many other former residents, fought for Japan. Russia was severely defeated and ceded all of Sakhalin Oblast to Japan.
Then, in the Third World War, Reimu and other former residents aided Japan against Russia and its allies. With Co-Operation from the European Union and the Republic of China, they launched an invasion of Russia in 2107 and managed to defeat it four years later.
A few years after the war, Reimu got involved in politics and was later elected as Prime Minister of Japan for her first time in 2138.
In Year 800,000,000, she, along with some other Earth residents (mainly from East, South East, and South Asia), begun to relocate to the recently established Neo Gensokyo in the Sunflower Galaxy and became President a few months upon arrival.