Kasumi's Marriage Hunting Grand Strategy: 2 and 1/2

In 2030, the Japanese archipelago is transferred to Earth in the year 2100 AD, where the male-to-female ratio is 1:520. The men of the alternate world Earth are becoming extinct due to Y chromosome deficiency. Within an alternate world order still dominated by imperialism. The South American Choir Nation declared war on the transferred nation of Japan. In the central Pacific, wills of steel collide. Japan achieved victory together with the Greater Japanese Empire. However, that merely proved that Japan was a foreign object in this world… But somehow or other, Japanese people are doing fine. (´・ω・｀) Since this is a series, please read it in your spare time if you have the details.