I was more surprised someone thought the Queen Mum was still alive…
…then I saw that person was Polycarp 
Napoleon I was supposed to be crowned by the Pope, but at the last minute (as during the ceremony itself) he unexpectedly took the crown from the Pope and crowned himself.
The Japanese rulers used the title to assert their independence from China.
Chinese ideology held that there was one emperor under Heaven, and he lived in Beijing. The Chinese emperors claimed authority over the entire planet. To them, there were no sovereign states. The nominally independent countries were merely places where the emperor had not yet bothered to send an army to impose his will.
To the Chinese emperors, the monarchs of Japan, Korea, and Vietnam, and the lamas in Tibet and Mongolia, were merely local governors, administering their provinces on the emperor’s behalf. The regions on the periphery were far enough from the centers of power that Beijing did not do a lot of meddling in their day-to-day affairs. From the common peasant’s point of view, whether you were ruled by an independent monarch, or a Chinese vassal, was not particularly important.
Japan was far away, and protected by stormy seas, and relatively difficult to invade. So the Japanese rulers could get away with stuff that others could not. When dealing with emissaries from China, they did not overtly challenge the Chinese emperor’s claims. But when dealing with emissaries from other countries, they would insist that titles be translated using the same word for the Japanese ruler as you would use for the Chinese ruler. For European visitors, this meant “emperor”. One ruler wrote a letter addressed “from the Emperor of the Rising Sun, to the Emperor of the Setting Sun”. That was not quite insulting enough to start a war, but by Chinese standards, it was extremely impudent.
In the 19 Century, when the rulers of Korea and Vietnam publicly declared independence, and proclaimed themselves emperors, that was a huge deal. It had both political and religious implications. Such open rebellion against Beijing had not been attempted in several centuries. It was a visible symptom of the decline of the Manchu dynasty.