箱館戦争
The story begins during the Bakumatsu period of Japan in the last years of the Tokugawa Shogunate. It continues through the pre-Meiji period and refers to historical events such as the Boshin War, including the involvement of foreign governments, the Naval Battle of Hakodate, and the Meiji Restoration. There are also references to historical figures such as Captain Kidd, Saigō Takamori, Andō Shōzan, Oguri Kozukenosuke (Tadamasa), Geronimo, and Mark Twain.