Emperor would be the top title of the secular world nobility. That title, in English translation, would be "His Imperial Majesty". The Emperor would be Head of State over his own dominions, but not over anyone else's country. The Emperor of Japan does not rule over Queen Elizabeth.
The top religious position in the religious world varies by religion. The Pope is the Head of of the Roman Catholic Church, the Patriarch or Primate of Jerusalem of the Eastern Orthodox, the Dalai Llama of the Buddist faith, etc.
The Queen is addressed as "Your Majesty" first, and as "Ma'am" afterwards. The men of the Royal Family are addressed as "Sir", although they are styled "His Royal Highness, (the Prince of Wales, the Duke of Edinburgh, etc)"
The men with "Sir" before their first names are, in descending order Barons, Baronets and Knights. Sir Arthur Conan Doyle was dubbed a knight. Knighthood is not passed to heirs. Sir Charles Baskerville in "Hound" was a baronet. His title went to Henry.