Zemestan is the god of frigid, harsh winter. Winter is a test designed to weed out the weak. The strong survive by taking what they need. Zemestan is L-E. Priests must be L-E. Zemestan was always worshiped extensively in Kermaan, but the migration north has increased his following. Priests of Zemestan get along with the Prophets of Talkh so long as the sacrificial suicides are individuals deemed weak or undesirable. Priests of Zemestan follow the “Season” rules in the Priest’s Manual and have major access to War and Law from the Tome of Magic.
Zemestan is the older religion, and was worshipped extensively in the north before the Claacos came, especially in the kingdoms of Kermaan, Chogha, and Yazd. Zemestan demands tribute and sacrifice in order to stay his frigid hand. Winter is also the time when the weak are culled so the strong can be unencumbered. Talkh takes a more inclusive view of who is to be called to death, but you can see that there is overlap. We are all in the north now, but especially in the far north where life is harder, Zemestan has begun to give way to Talkh.
I think Talkh are the more dangerous of the two. While Zemestan demands appeasement and respect, Talkh demands the ultimate price. The greatest glory goes to his followers who bring the willing to his altar to dedicate their deaths to him. This particular practice has brought the Prophets in direct conflict with the followers of Izanagi.
As his influence has increased, Talkh has corrupted Kavusian lords who have taken to ordering some of their samurai to perform the rite of seppuku on an altar of Talkh. Some comply, but others see no honor in such a death and renounce their daimyos and become ronin, wandering the lands as swords for hire. Thus, Talkh is in direct conflict with Izanagi.
The Templars of Khoob are also sworn enemies of the Prophets of Talkh, and to a lesser extent Zemestan. Here in these caves, we priests of Wheyfus, Oetheni, and Anahita would tolerate a priest of Zemestan, but would drive out a prophet of Talkh. Winter is hard, but it is part of nature and is disrespected at your own peril. There is nothing natural about death for death’s sake.