In 1782, Shimabara was struck by a lightning storm. Shimabara and the surrounding areas began to change after that storm, with Castle Shimabara becoming more and more sinister. Amakusa Shiro Tokisada, who had been killed by government forces, has risen from the dead to build his own vision of the world.
Samurai Shodown 4 gives players 17 characters to choose from, including Amakusa himself. After choosing a character, players must then choose slash or bust mode. Slash mode characters are the default and play similarly to their previous incarnations. Bust mode characters are darker and sport a somewhat different set of techniques.
Players must also choose from one of three grades before starting the game. Beginner grade characters can perform automatic knockdown combos and desperation moves simply by pressing button combinations, but suffer from having power meters that charge more slowly. Upper grade characters are significantly faster, but lose the ability to block attacks. Medium grade characters are the default, and have no advantages or disadvantages.
Character power meters are charged through attacks, and when full can be used to execute powerful desperation moves. Other new options include the ability to commit suicide and give up the round in exchange for starting the next round with a full power meter, and the ability to voluntarily throw weapons away as a taunt maneuver.