This is a disease that evolves people into crabs. A particular coastal village in the continent of Glaive, Persevera, is subject to this ancient disease. Noone truly knows how people get them, but for sure it came from the sea. People who venture out too far out or too long at sea sometimes wash up ashore already afflicted with this disease. Over the course of several weeks, they will evolve into crabs. There are benefits to being a crab, so it's not all bad. I talk more about this in my YouTube channel.