Beast Convergence
Alongside recovering from the ramifications of having used a forbidden technique, Rui also took the time to research the Beast Domain thoroughly. Regardless of the responses from the four avenues of inquiry, he would be entering the Beast Domain to find the Divine Doctor, but that didn't change.
While he wasn't training, he took it upon himself to familiarize himself with the Beast Domain.
It was only then that he realized that although the borders of the Beast Domain encompassed much were defined on map, the exact location where the Human Domain ended and where the Beast Domain began were not entirely clear.
It was more like a gradient.
When one reached the core of the domain, the Human Domain became increasingly scarce, while the Beast Domain became increasingly abundant. On paper, the Beast Domain was defined as the perimeter formed by the points where human settlement ended.