After seeing the information on the third stage of the Main Quest, Su Xiao understood that the Great Sage's soul chain had first been extracted from outside the container and replaced by a Secondary Goddess named Shataye.
No wonder the Great Sage had managed to hold on and maintain his peak condition. The one directly being eroded by the ancient god's energy was no longer his soul chain, so of course he advocated maintaining the status quo.
The news circulating outside was that the King of Light, the Great Sage, and the Spider Queen had sacrificed themselves to seal the ancient god. This gave the Great Sage unimaginable prestige among the beast tribe. Even the beast tribe members who did not support him still respected him.
Once the seal was opened and only the Great Sage remained alive, his prestige among the beast tribe would plummet, and he would face all kinds of doubts.
For the Great Sage, this would be a tremendous loss. He needed his current prestige to accomplish something. It could be said that the current Great Sage was half the ruler of the beast tribe—and he ruled not through force, but through prestige.
To open the seal, Su Xiao only needed to find the Secondary Goddess, Shataye, and sever her soul chain. After that, he would return to the White Town and sever the King of Light's soul chain. The seal would then be completely opened.
Su Xiao guessed that the Secondary Goddess Shataye's soul chain should have the same soul fluctuations as the Great Sage's. That was why it could replace the Great Sage and coil around the outside of the container. Severing the Secondary Goddess Shataye's soul chain would inevitably affect the Great Sage.
The Secondary Goddess Shataye was within the beast tribe's territory.