I read that the Emperor of Japan is the only monarch currently going by the title of emperor, but I was curios why. Japan is not an empire, but I understand that it was a term used to help differentiate him from the Shogun for westerners. But what I don't understand is why the Kinds or Queens of Britain never took on the title. I know that Victoria was considered the Empress of India, but that title seemed to be less important than Queen of England. Was there any reason the title was not upgraded to Emperor?
At the time of the Union between the Kingdom of Great Britain and the Kingdom of Ireland in 1801, George III was asked whether he would like to change his title to "Emperor of the British Isles" but he said he was satisfied with the traditional title of king.
When Disraeli made Queen Victoria Empress of India in 1876, this aroused opposition from some Liberals who claimed that the title "Empress" was un-English and was associated with despotism. Disraeli, who had always seemed exotic to his contemporaries (being a descendent of foreign Jews), was attacked on anti-Semitic grounds as an Eastern corrupter of the English crown.
Victoria was made Empress in India only; she retained her title of Queen of the United Kingdom. Victoria wrote that the title was "best understood in the East, but which Great Britain (which is an Empire) never has acknowledged to be higher than King or Queen". Victoria was happy to retain her traditional title within the UK but abroad she wanted to the title Empress as she knew her daughter in due course would be titled Empress of Germany and she did not want to be outranked by her children.
In short, there was no demand to change the traditional title of King/Queen into an imperial one. Being titled Empress of India left Victoria still in her title of Queen of the United Kingdom and this was satisfactory to the country. To change it to an imperial would have aroused strong opposition from Liberals on grounds that it was a foreign-sounding title with strong connotations of absolute monarchy such as Imperial Russia.
Source: Oxford Dictionary of National Biography.