When anon was called a "witch master" and the snakes wanted him to use the Anathema to "destroy things", they never explained why or what it meant. A number of people tried to banish "the boy" which was assumed to be a possessing spirit, but no matter what was done, he kept coming back. After original anon left for his astral temple along with his snake cult, Gensokyo placed a new black cat in his body to uphold the position, "because it's an important position that must not be lost". But they didn't explain either.
So, the answer is: it is a position of having the genetics of an ancient witch-master family line, and an especially beneficial one, even if anon's life in modern terms does not look special. The voice heard which would not leave, is the effect of being a perfect channel, of the egregore of Latin America. That is the reason why his Anathema is so insanely powerful, it's channelling an entire continent, which has a long occult history.
The pyramid which was located in south of Brazil is part of a system of 5 pyramids world wide, and this one itself is essential for functioning of the world also. The people in there were a hive of genuine sub-humans possessed by a hive of evil spirits, but they are able to perform Aztec style rituals correctly, and a god is protecting them because they are a ritual artifact.
We made used of them to fix the connection to the egregore, by performing a ritual called "sacrifice of the evil king" where the representative of the opposing point of the egregore is killed, which returns control to the witch master in a positive manner. The god appeared at the scene, giving his approval, and there was a change to the egregore itself instantly after.
