There were many Koreans in Japan when Japan surrendered - about 1 in 30 people in Japan were Korean, and they were concentrated in industrial cities and regions.

The pre-war (1937) Korean population in Japan was about 2/3 million. This increased greatly during the war, as the diversion of Japanese workers into the army and navy produced a labour shortage. Some Koreans faced with poverty and shortage sought work in Japan in the hope of improving their position. Others (about 2/3 million) were conscripted and taken to Japan for forced labour. The Korean population in Japan peaked in 1945 at about 2.4 million. The post-war Korean population in Japan quickly dropped to about 2/3 million, about the same as the pre-war Korean population, after most Koreans had returned to Korea.

The number of Koreans in Kure isn't known precisely. There were about 80,000 Koreans in Hiroshima prefecture at the end of the war (and possibly up to 30,000 Koreans died in the atomic bombing of Hiroshima). Kure certainly had substantial numbers of Koreans.

Many of these Koreans would have been in favour of Korean independence. Some would have been tipped towards Korean independence by anti-Korean discrimination in Japan, and some by being conscripted for labour. In some cases, Korean independence activists moved to Japan to avoid the Japanese police (because they were known by the police in Korea, and not by the police in Japan, and would be safe in Japan as long as they kept quiet). The flag of the Provisional Government of the Republic of Korea, based in China, was very similar to the modern South Korean flag:

• Provisional Government: https://commons.wikimedia.org/wiki/File:Flag_of_the_Provisional_Government_of_the_Republic_of_Korea.svg

• South Korea: https://commons.wikimedia.org/wiki/File:Flag_of_South_Korea.svg

This is the flag that would have been raised at the end of the war, by independence-minded Koreans who supported the Provisional Government.

Some final comments:

• Only about 12% of Koreans conscripted for labour ended up in Japan. Most worked in Korea or Manchuria (Manchukuo). Some worked in war zones, with very high death rates in some cases. In total, almost 6 million Koreans were conscripted for labour. About 200,000 Koreans served in the Japanese armed forces, some volunteers and some conscripts. For more on WWII conscription in Korea, see https://www.reddit.com/r/AskHistorians/comments/jjq5gt/did_were_nonjapanese_people_conscripted_to_fight/

• For the rapid rise of the number of Koreans in Japan, see the following figure. Note that this is the number of registered Korean residents and is lower than the actual number (as noted above, peaking at about 2.4 million): https://commons.wikimedia.org/wiki/File:Population_of_Koreans_in_Japan.gif

• The short-lived People's Republic Of Korea, which declared itself the government of independent Korea after the Japanese surrender in 1945, outlawed in the American occupied zone (the future South Korea) in December 1945, chose a different flag: https://commons.wikimedia.org/wiki/File:Flag_of_the_People%27s_Committee_of_Korea.svg