I think that Humakti don't have magic to "destroy" ghosts per se, but to sever the link between a disembodied spirit and the mundane world. (I'm not sure they have the same power over "daimones" ... still thinking on that one). I think this fits with their mythic role and with your ruling. This suggests the Humakti magic won't work on the same spirit in the spirit world, or on sprits that are supposed to be their (dryads, wyters, regimental spirits) ...?
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