The Rot is a disease and major plot element in the Strafe series. It is spread through physical contact with the skin. Victims of the Rot are known as "Rotten", and live in the Rotten District of Noah which is kept under strict quarantine to prevent the contagion of the disease.
In the New Fantendoverse, it still exists within Noah with it's own district. It is mentioned during Strafe: Warzones and Leah plans to find a cure for it but got horribly sidetracked and seems to have forgotten about her plans to cure it as the story ends.
In the Mynisverse, it is not isolated to a single district, and is instead found throughout the country of Noah. The Twisted Cross has recently developed a cure, but is asking for a very high price for it; and even then, it doesn't always work properly.
The Rot causes the host's body to slowly decay over time, reducing their life expectancy by a large time. A host of the Rot can be identified by their pale grey skin colour, hair loss, and a lack of fingernails or toenails.
In the latest stages, the host's nose, ears, fingers and toes are likely to simply fall off before they die a short time afterwards. Some hosts in the Mynisverse, like Strafe, have even lost whole limbs to the final stages of the disease.