At the moment, many people are unfamiliar with the name East Prussia. Because East Prussia has become a historical term. The main area of East Prussia, now called "Kaliningrad", is an "enclave" of Russia. "East Prussia" was occupied by the Soviet Union after World War II, and the Soviet Union divided the land into three parts, one of which is today's Kaliningrad Oblast.
Similar to the fate of "East Prussia", there are also the four northern islands of Japan. After World War II, Japan frequently demanded the "Four Northern Islands" from the Soviet Union (and Russia), but in contrast, it never saw Germany ask the Soviet Union for Kaliningrad.
Questions of international relations
After World War II, Germany was divided into East and West Germany. East Germany could basically be seen as a puppet state of the Soviet Union. East Prussia was closer to East Germany, so East Germany would not be dazed enough to beg the Soviet Union for East Prussia. After the reunification of germany in the 1990s, due to the passage of time, the unification of Germany did not have a reason to ask east Prussia.
Japan is different. After the war, Japan's homeland was occupied almost entirely by the United States. The post-war world fell into a state of the Cold War. To this end, in order to contain the Soviet Union, the United States chose to support Japan. With the support of the United States, Japan was emboldened and began to ask the Soviet Union for the four northern islands in the 1950s, and it is still demanding it today.
Geopolitical issues
The four northern islands are very close to Japan's hokkaido island, and in terms of geography, they can be connected to the Japanese mainland. East Prussia is different. Although Kaliningrad Oblast is an enclave for Russia, even so, Russia's distance from Kaliningrad Oblast is much closer than germany's native land to East Prussia, so Germany's claim to East Prussia is undoubtedly a thankless task. This is one of them.
Second, the territorial dispute between Japan and the Soviet Union (Russia) is clearly the four northern islands. East Prussia was different – because East Prussia was not annexed by today's Russia, but was divided into three countries. Even if Germany had the heart to beg east Prussia, it would inevitably befriend three countries at the same time. For this alone, germany's maneuverability in asking east Prussia was minimal.
Demographics and obsessions
Russians are very "experienced" in the management of the population. For example, china's Outer Northeast region, under Russian rule, can no longer find traces of China; and when Stalin was alive, Stalin feared that the Goryeo people in the Outer Northeast would become a force to harm the Soviet Union under the manipulation of the Japanese, so he uprooted the Koryo and sent them to Central Asia.
Similarly, in the homeland of East Prussia, there are not many traces of Prussia. Therefore, this made the Germans feel that there was no need to ask for this land.
Of course, the demographic structure of the four northern islands is also dominated by Russians, but the Japanese feel that even so, Japan has the need to beg for the four islands - after all, for Japan, no island can give up, which is an obsession!