Fall of the Samurai : British Invasion.
"Prepare for the Sepoy hordes of the British Army as the Policeman of the World comes to bring the Boshin War to a rapid conclusion. The Imperial and Shogunate forces must fight side by side to prevent the 'Wooden Wall' from encircling Japan. Forever removing the title of Emperor from our shores."
(Cue Japanese flag with poorly photoshopped/rounded Union Jack replacing the red dot, carried by wave after wave of Sepoys and British soldiers).
"Or will you fight as the British under Sir Robert Napier, enforcing stability on the Japanese islands, and fight for British Honour! It will be a hard job, whilst reinforcements are coming, it will be local resources that pay for this expedition. Can the Royal Navy, Indian Sepoys, and Kirishitan Samurai bring peace under a new, British Shogunate?"
Amusingly, writing this, the Tokugowa Shogunate may start at war with Britain, but may eventually surrender and work with Britain if they were assured power. The Emperor is the only person who has everything to lose here, it would be the end of the Chrysanthemum Throne, or at least, no Japanese person would sit in it until independence.
And at the end of the war, with peace assured, a new crowning ceremony in Kyoto, where the terrifying words are spoken as Queen Vic rises from the Chrysanthemum Throne.
"All rise in the name of Queen Victoria - Queen of the United Kingdom, Empress of India, and Empress of Japan."
(and then the throne is shipped to Britain, where like the Elgin stones, it hasn't a chance of leaving the British Museum)