The Samurai would shave the middle part of his head, called a chonmage, where the remaining hair was oiled and waxed before being tied into a small tail folded onto the top of the head in the characteristic topknot, so that his helmet (kabuto) fit tightly onto the head when donning his armor for battle. With less hair, the samurai would also not suffer from the buildup of heat on the head when wearing the helmet.
The Treaty of Tordesillas was an agreement between Spain and Portugal that was signed in 1494, in the namesake town in Spain. In this treaty, Spain and Portugal agreed to divide the New World between themselves for colonization, conversion, and administration by setting a line of demarcation that had ran from north to south at a meridian about 370 leagues (one league is equal to three miles) west of the Cape Verde islands. Spain would be granted everything to the west of this line, while Portugal would receive everything to the east. This corresponded roughly to most of eastern modern Brazil and Africa being conceded to Portugal, while Spain would take the rest of the New World. It would later be revised by the Treaty of Zaragoza (1529), which included Asia, since neither party had considered the world's spherical shape at the time of drawing the line of demarcation, and they quickly realized they would need a second line to divide the world into two hemispheres. The Portuguese hemisphere included Japan, as well as the rest of Asia to the west, leaving Spain with most of the Pacific Ocean but none of mainland Asia, with the exception of Spain given the right to trade in the Philippines. Though the treaty was largely ignored by other European powers, particularly when the Protestant Reformation took root, Spain and Portugal followed it fairly faithfully, though it did require some amendments as more of the world was charted.
Shoji in Japanese architecture refers to the sliding doors and windows made of a latticed wooden frame covered in translucent white paper. In summer, Shoji doors are often completely removed to open up the house to help alleviate the humidity of the season
William Adams, the historical figure which the character John Blackthorne was based on, spoke a number of languages, including Portuguese.
Portuguese was among the world's key languages in the 15th and 16th centuries, serving as the lingua franca (lingua franca refers to any language used to establish communication between people whose native languages are different) in several regions, including in African and Asian countries. Portugal was ahead of all European countries when it came to maritime imperialism in the early 16th century, establishing commercial routes and colonies in North Africa, West Africa, South Africa, and the region that would become known as Brazil. The Portuguese arrived in Japan in 1543, and by the end of the century, both the Portuguese language and the Christian religion had been assimilated by many Japanese. Whenever Blackthorne is speaking in English to a member of the indigenous population, they are speaking in Portuguese within the story. Although John Blackthorne is indeed English, he only communicates with the Jesuits using Portuguese. The show uses English in place of Portuguese to appeal to a wider audience.