"Sanada and Jarvis will play the male leads, Yoshii Toranaga and John Blackthorne, respectively, in the project, which tells the story from both a Western and Japanese perspective... Written by Justin Marks and Rachel Kondo, Shōgun is set in feudal Japan. It charts the collision of two ambitious men from different worlds and a mysterious female samurai: John Blackthorne (Jarvis), a risk-taking English sailor who ends up shipwrecked in Japan, a land whose unfamiliar culture will ultimately redefine him; Lord Toranaga (Sanada), a shrewd, powerful daimyo, at odds with his own dangerous, political rivals; and Lady Mariko, a woman with invaluable skills but dishonorable family ties who must prove her value and allegiance.
... Sanada’s Yoshii Toranaga is a living legend. He is a powerful daimyo from a feared lineage, isolated and outnumbered by his enemies in Osaka Castle when the story begins. But little does anyone realize that Toranaga is a brilliant strategist, a master of the long game, and the holder of Japan’s ultimate fate. Jarvis’ John Blackthorne is a restless English pilot in search of a destiny far from the world he was born into. His mission is to forge a path into the Pacific islands and disrupt Portuguese and Spanish interests in Japan. But Blackthorne finds more than he bargained for when his ship washes ashore within the territory of Toranaga, a deadly warlord who becomes his captor and spiritual mentor."
They haven't cast the third role, for the female character; the head-writer Justin Marks has credits on the live-action Jungle Book movies and the forthcoming Top Gun sequel so, uhh... we'll withhold judgement. He also did a TV program I've never heard of, something called Counterpart that starred JK Simmons and Olivia Williams? There is so much TV now, you guys. I have no idea.