Greater part of Japanese people consider that their Emperor is essential for the synthesis of Japanese nation. I think their idea is the truth and what enables the successive Emperors to hold together Japanese people is the Korean origins of them.
Japanese people is properly far from the civilization. In fact, in the ancient age, they were the very barbarians who collected nuts as daily food, never clothed themselves, neither read nor wrote, and inhabited tiny villages of at most 30 companions; moreover these villages of them would never communicate with each other except the war. Like so, they seemed to be the last people who unite themselves into one country.
Jinmu the great, the first Emperor of Japan, came from Korean peninsula with his iron-armed cavalry, conquered all proto-Japanese villages by the ethnic superiority of his Korean origins, thus he has brought together Japanese people; this historical fact is often called “the Korean Conquest” compared with the Norman Conquest in England.
He also has taught Japanese people the literacy, the ironmaking and the law, everything that comprises the civilization, and after his death his successors also led Japanese people into the progress, including the modernization in Meiji era. Therefore, Japanese nation and people has been developed by the successive Emperors and their Korean ethnicity, “Koreanity.” Hence, it’s plausible thought that if Japan abolishes his monarchy, the help of Koreanity will disappear and Japan will break out into many tribes like as the prehistoric Japanese were so.