Kensi is a set of free wargames rules for samurai warfare ranging from skirmishes to large battles. The rules include a fantasy element, and the world is a not-quite-historical Japan.
Samurai Knight Fever is a set of free wargames rules for Japan’s Age of Battles: 1550-1615. The author is Tod Kershner, who is the designer of popular and established wargames rules including Warfare in the Age of Reason, Age of Discovery, Age of Napoleon, Pig Wars, A Firebell in the Night and Iroquois Terror.
Kershner is a friend of mine, and I have long enjoyed playing in his games.
Samurai Blades is one of a series of board games published in 1984 by Standard Games and by now long out of print. The game was essentially a skirmish game played on a hex board, with cardboard miniatures. Each character in the game was represented by several pieces, each depicting a different level of damage and injury. The web page at the link has lots of resources for the game, including the rules and gifs, tiffs, and jpgs of the pieces and boards. This is really useful if you have the game but have lost one of those aforementioned damage markers.
Given the high levels of current interest in games set in Shogunate Japan, I thought people might be interested in these hand colored photographs of Japan from 1865. That’s several hundred years after the period in question, but I should think they would still be useful.
A Most Honorable Victory is a set of free wargames rules for miniatures games set in 15th and 16th century Japan.