Unit 666 is a covert biological research and development unit of the Imperial Jingdaoese Army which researches and compares the DNA and ethnic traits of the Jingdaoese people. It was active in Alduria in 1674 AN to investigate the nuclear wastelands and attempt to clean it up.
In the past their research was used to investigate why some Jingdaoese, like Yuan Windsor, rebelled against the Imperial Household and Heavenly Throne. It was believed this was not solely because of them being culturally influenced by outsiders, but also a result of an error in their DNA.
The research results were later stolen and used by private companies, who sought to enhance simple Jingdaoese and turn them into super soldiers. One of those investigations led to the outbreak of a mutant virus, which ultimately led to the death of the Danya Emperor in battle and the rise of the Geming Kingdom.