Seer Tanapi:
If you kill a kasha bear, you must cut open its abdomen and take out the Kasha Parasite. The evil spirit kasha contaminates the gray bears through the parasites.
But the true enemy to defeat is the kasha totem spirit. They say that the evil kasha spirit takes the form of the gray bear. Based on my studies, if there are enough parasites, they will call forth the kasha totem spirit. I don't know how many are needed though.
If you kill the kasha totem spirit, the crystal of the kasha totem spirit will appear. Bring it to me. It is something I desperately need for my studies. If you bring it to me, I will reward you in the name of the Hestui. Good luck.