Because seven years ago, the steam fleet of the United States knocked on Japan's national gates.
Given the presence of a steam fleet and the invasions by Western powers... the time period is likely the mid or late 19th century.
Not long after the establishment of the Shogunate, to ensure national stability, the Shogunate issued the National Lockdown Order, leading Japan into a state of isolation, maintaining contact only with China, Korea, and the Netherlands.
Under the National Lockdown Order, Japan enjoyed over two hundred years of peaceful times.
Until... Kaei 6 (1853), seven years ago, when U.S. Navy Commodore Perry led a fleet to knock on Japan's gates.
Because Perry's fleet included black steam battleships, the event was called the "Black Ship Incident."
Ancient society Japan couldn't possibly be a match for the United States, which had undergone the Industrial Revolution.
Forced by the might of the United States, Japan was compelled to accept the Japan-US Amity Treaty.
Japan's gates, thus, were wide open.
The "Black Ship Incident" had an enormous impact on the Shogunate officials and citizens alike.
Some saw the gap between Japan and the overseas powers and proposed to learn from the advanced systems and technologies of the Western powers, just as they had comprehensively learned from the great eastern nation a thousand years before, advocating "Restoration" and adopting the barbarians' strengths to make Japan strong.
However, those in Japan holding this concept of "learning from the West"... are pathetically few.
The nearly 250-year-standing "National Lockdown Order" made the Japanese, from the leaders to the common folk, narrow-minded and arrogant.
Faced with the advancing Western powers, the most popular and widely embraced idea among the Japanese populace is — all these foreigners are nothing but barbaric savages to be entirely expelled!
Fight! Fight! Fight!!
Those advocating for the expulsion of Western powers shout the slogan "Jōi." Therefore, these advocates are collectively called the "Anti-foreigner Faction."
"Jōi" ideology is now the most mainstream thought, without exception.
The "Anti-foreigner Faction," advocating for the expulsion of foreigners, is currently the undisputed majority, while those advocating for peaceful coexistence and learning from the foreign powers are entirely in the minority.
Though all those advocating "Jōi" are known as the "Anti-foreigner Faction," within this faction, many different ideological sub-groups exist.
Some people's views are relatively mild, advocating the peaceful expulsion of Westerners.
However, the vast majority of the "Anti-foreigner Faction" advocates using force to drive out all powers, led by the United States, without exception.
Over the past seven years, as more foreigners set foot in Japan, some in the violent Anti-foreigner faction have become increasingly radical and extreme.
As of today, within the "Anti-foreigner Faction," such a voice has even emerged: those who admire the West, think well of Western things, or work for Westerners, are national traitors enamored with the barbarians! Such traitors also deserve death!
Surprisingly absurd and extreme ideas have gradually spread and are increasingly regarded as a code of conduct by many.
The three samurai who just attempted to assassinate Aoto belong to this radical Anti-foreigner faction.
Why did the radical Anti-foreigner faction target Aoto?
The reason boils down to the fact that "Original Tachibana Aoto" worked at the United States Embassy for seven days more than a month ago.
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The protagonist Tachibana Aoto is pronounced as: Tachibana Aoto in Japanese.
The Romanized spelling is: tachibana aoto.
Thus, Aoto's full name looks very short, consisting of just three kanji, but the pronunciation is quite long, stretching to a full seven syllables. The surname "Tachibana" alone takes up four syllables.