T-Virus

The T-virus (Transgenetic Virus) was a lethal disease that originated as a side effect from Terraforming the earth. After the Ancient Humans have built their infrastructure with the new and versatile element, they soon fell victim to a mutated Megavirus that had a steeo death rate, all the survivors would then be mutated into the fenguli, and eventually the modern Martians that inhabit the planet.

Origins
The T-Virus was first identified 53 years after the completion of Mars' habitats. The disease caused several colonists to become deathly ill, and while symptoms varied drastically, All of the cases included some identification of radiation poisoning.

Nature
It was later revealed that the T-virus attacked its host's DNA, and that the terraforming the Ancient Humans built their planet with was responsible for the T-virus' deadly mutation because of the megavirus was unintentionally mutated into the T-virus. Any survivor sees a rapid transformation in their entire genome to a point where they are no longer considered human, but martians instead. These martians are now able to survive in the harsh climate of Mars without any assistance from technology, they lose all their hair and their skin color turns green, and became immune to any further radiation poisoning, but at the cost of their memories. These martians, scared and confused, left the space colonies and formed the Fenguli Society deep in the caves of Mars.

Alternate Counter-Measures:
Most of the Ancient Humans efforts to cure the disease proved futile, and after seeing a drop in 30% of the colony's population, the colony's top scientists began the Ascension Project. The ascension project was designed to upload the consciousness of humans into mechanical bodies in order to keep some human presence on Mars. The project was a success and some humans were able to transfer their minds into machines, leading to the Ascended. Who then laid dormant for centuries until being discovered by the Fenguli.