This spell causes the Earth kami within a physical object to abandon that object, weakening its physical strength. Wood warps and flakes, stone and metal turn weak and brittle, cloth becomes thin and fragile, and so forth. The spell’s effects are permanent.
Mechanically, any weapon which is affected by this spell will lose 2k1 from its DR, and any armor will lose 5 from its Armor TN bonus and 3 from its Reduction. A variety of other non-mechanical effects can also take place, subject to the GM’s adjudication - for example, a kimono affected by this spell will rip if it is subject to the slightest tension or stress, and a scroll will tear and crumble the moment it is unrolled. Weakened stones or beams could be used to sabotage a bridge, to facilitate breaking into a besieged castle, and so forth.
In general, this spell will not affect awakened items (e.g. nemuranai), since their empowered spirits resist the shugenja’s entreaty.