Basically, they're a combo of anticiv, polytheism, and ecosocialist theory. They worship the Nine Primogenitors (sometimes each to different degrees) while ignoring lesser gods; sometimes includes cannibalism depending on how primitive the specific Xivisti tribe is, with other varied values held between tribes.

Feralism, Primitivism

When scientifically advanced creatures came to Daeji and allowed Daejiin access to technology, many Daejiin rejected the technology and became paranoid that it would harm the species, so they left the villages with the new technology and created their own tribes in the wild. Over time, these tribes evolved to become more savage than the average Daejiin, and there are a few who worship the Primogenitor Decay above all else, and they often perform cannibalistic rituals, eating parts of their own members' bodies.

Technology causes emotional and physical harm over time, and life should be lived with real interaction. The natural cycle of life also includes predator and prey interactions, even if this means hunting your own species.