During a school cruise, a group of friends is transported back to the year 1636. Historical records indicate that the Shimabara Revolt erupted in 1637. This uprising, led by the charismatic youth Amakusa Shirou, consisted of Christian rebels and concluded with their defeat, claiming 3,000 lives. The protagonist, Hayumi Natsuki, is mistaken for Amakusa Shirou by the villagers she encounters, despite the historical figure being male. It appears the actual Amakusa Shirou had died the previous year, before achieving recognition or popularity as a leader among the populace. Soon after, she gains fame as a sort of heaven-sent angel, and people begin calling her "Shirou," believing her to be the savior prophesied 25 years earlier.