As mentioned above with the Nezumi, the Taint causes humans to go mad and, at high levels, can physically deform them. The Taint can be contracted through environmental exposure (traipsing around the Shadowlands for long periods, the aura surrounding powerful Oni, certain tainted spells) or by direct contact with tainted items/creatures (an oni's claws, a magically tainted hair comb, a drop of a tainted human's blood in your food or drink). Crab soldiers wear fingers of jade (a rod of jade about the size of a finger) to protect themselves from environmental taint; the purity of jade is the antithesis of the Taint and it draws the Taint into itself. Jade slowly corrupts from a hard green stone to a soft, black clay as it absorbs the taint. Jade also possesses the ability to overcome the formidable powers and defenses of the Shadowlands Horde; highly magical weapons, treasured among the Crab clan, are either made of jade or function like jade against the Horde. Purified crystal is a stronger, more concentrated form of jade.
Kuni shegenja are experts at detecting the taint and they perform the cleansing rituals that follow engagements with the Shadowlands (and human forces; blood and corpses are not inheretly tainted but they are considered unclean). It should be noted that, once a samurai has reached a certain level of taint, he becomes forever marked by it. Only substances and rituals of legendary proportion are able to cleanse such an individual. Tainted Crab are placed under the watch of a Kuni Witch-Hunter, a group of shugeja and bushi who police the Crab for hidden taint and the practice of maho. Witch-Hunters ensure that tainted Crab do not lose their minds and attack the Crab from within; at the first sign of madness, a Witch-Hunter will cut down his charge and remove his head.
Human corpses in the Shadowlands are exposed to the Taint and many rise as undead. In the past, Crab sorties knew the horror of losing half their number only to see them rise up against them. It provided the Shadowlands with a further numerical advantage and proved exceptionally demoralizing. Since those days, the Crab have accepted that they must behead their own brothers when they fall in battle. When a samurai is too injured to make it back, he will ask for an honorable death; it is far preferred to serving the dark powers he and his ancestors have fought for 1000 years.
Finally, there are some samurai who have embraced the Taint and the Shadowlands. Maho-tsukai, practitioners of blood magic, call upon kansen, or evil elemental spirits, for their magic. These kansen are tainted and the very act of casting blood magic can taint the maho-tsukai. Though driven mad, these shugenja are also "gifted" with powerful, physical deformities like claws or wings, furthering their grasp for power at any cost. Most maho-tsukai in the Empire practice in hiding, for maho is a capital offense and magistrates in each clan, along with the Emperor's Jade Magistrates, ruthlessly hunt them down.
More striking than maho-tsukai are the Lost, the twice-cursed samurai who abandoned their rightful lords to serve Fu Leng. Daigotsu is the self-proclaimed high servant of Fu Leng, the Ninth Kami. He established the Lost within the Shadowlands and repeatedly makes bids against the Empire for shunning his Dark Master; his argument is that Fu Leng is just as worthy of worship and followers by divine right as the other eight kami and he and the Lost should be considered a Great Clan with full participation in the Empire. He is, of course, considered mad and blasphemous. The Lost range from the fully mad and deformed to those tainted samurai who are indistinguishable from regular people. Many live in the City of the Lost hidden deep within the Shadowlands but many also maintain their regular lives within the Empire, gathering information, weakening defenses, and tainting key officials within the clan and imperial governments.