The Dark Samurai were revived by the vengeful spirits of those who opposed the Tokugawa family. Their purpose of their revival was to destroy the Chingo Stone, which protected Great Japan from unstable Qi.
However, the Dark Samurai, who weren't even aware of why they revived, showed more interest in battling strong opponents, much to the spirits' frustration.
None of the Dark Samurai were complete revived; as a result, all of their bodies have lost a certain ability.
To compensate for this, their bodies were given equipment that mimics the abilities that their bodies have lost. Although this equipment doesn't completely compensate for their handicaps, some of the dark samurai can use it unique ways to enhance their fighting abilities.