Yamada: The Samurai of Ayothaya

Attacked and wounded by a group of traitorous Japanese who disguised themselves as the Hongsawadee soldiers, a mercenary samurai named Yamada Nagamasa is rescued and nursed back to health by a group of Siamese warriors in service to the King of Ayothaya. Confused by the mysterious identity of his assailants, Yamada stays with the warriors, befriending them, learning their art, and eventually pledging his loyalty and life to their cause and kingdom.
(Source: Wikipedia)