In an alternate-reality 16th century feudal Japan re imagined with magic and advanced technology, an African man named Yasuke went from being in the service of Jesuit missionaries during the Nanban trade to being a warrior and retainer in the service of Lord Oda Nobunaga. In the year 1582, he witnessed the fall of Nobunaga’s forces in battle at Honnō-ji Temple against the army of the Dark General, who serves the demonic warlord Yami no Daimyō. With Nobunaga’s death and the defeat of his forces, Yami no Daimyō assumes complete control of the land. Twenty years later, Yasuke tries to put his storied past as a legendary ronin known as the “Black Samurai” behind him and retires as a recluse boatman named Yassan at a remote village. He encounters a singer at a local bar named Ichika and later agrees to take her and her daughter Saki, a sick girl with mysterious magical powers, north to see a special doctor to help with Saki’s condition. After an attack by mercenaries who are after Ichika and Saki, Yasuke is tasked with protecting Saki while coming to terms with his past, dealing with would-be conquerors of Japan, and facing dark supernatural elements as Yasuke and Saki find themselves in the middle of a struggle against the forces of Yami no Daimyō.