The Giant Domain and Human Domain were neighboring Sectors. It only took Damien a day to reach the boundary between them.
The main problem was the turbulence that existed at the boundary.
Several tens of millions of kilometers of destroyed space, like a diluted representation of the Abyss, separated the Human Domain from everything around it.
While it acted as a nigh impenetrable defense against outside forces, it was also the very cause of the Sector's decline.
Naturally, this portion of the universe healed considerably over the past 10,000 years, so it was only powerful enough to hold off against enemies under the extreme peak of 4th class, but that was more than enough.
After all, the Human Domain also had its experts. They would only lose if the other side could abuse a numbers advantage.
And even then, they would have much time to prepare while the able forces made their way through the spatial chaos!