What kind of plague was it?
About sixty years ago, many demons in the Speedcar Nation suffered from an extreme panic disorder, unable to eat or drink for many consecutive days, then turning dark in complexion, vomiting and having diarrhea, unable to move, and then they would die.
Whenever they recovered a certain population, this situation would reoccur.
Why would they panic?
The locals said it was because they were bewitched by an evil god, which caused the panic, leading to sickness and death.
"Demons who died from the disease would become sacrifices to the Evil God."
However, Ma Lin conducted an investigation and discovered that it wasn't the work of an Evil God but a viral cardiac illness, highly contagious among the lower-class demons. It was deceiving at first, appearing to be a mild disease, but once it turned severe, the mortality rate became very high.
This illness could be cured with some common antibiotics on Blue Star.