Black Blood Town was a small town that was situated right in front of the Ancient Ruins.
The Ancient Ruins actually covered a wide, vast area, with plenty of Mutant Plants, Mutant Beasts and other life forms that lived within. Terrifying biological creatures could be encountered when inside, and even a Type 4 Divine Warrior could fall if not careful.
However, there were plenty of resources that could be found within, even clean water, other legacies left behind prior to the apocalypse, hence, many were willing to risk their lives to explore the ruins.
Black Blood Town was a sort of a stop that humans had established right outside of the ruins. The town came about because there were 5 wells in the town, each of them containing water of radiation level 2. Because of the water sources, this Black Blood Town quickly flourished.