Mao is a contractor that has the ability to take over the bodies of animals. He lost his original human body and is now confined to the body of a cat.
Mao is a member of the Syndicate and acts as a reconnaissance operative for the group.
After losing his original body, Mao now resides within a cat. Because the cat's brain is not fully capable of maintaining a human conscience, Mao is linked to a syndicate server where he must frequently download data in order to maintain control of the cat. Mao's messier code is HM-432.
Mao is the only member of the group that actually thinks like a contractor, using logic in most situations. However, he has willingly chosen to protect his partners by keeping information from the syndicate on more than one occasion. Mao states that he finds Hei's behaviour fascinating and that he is never boring to watch.
Mao is one of few contractors that does not need to pay a price. This is because Mao lost his original human body and therefore, his contract has already been paid.
At the end of the first season, whilst enterting Hell's Gate with Hei and Yin, Mao loses his link to the Syndicate servers and cannot maintain his human conscience, saying a very brief goodbye before the cat's consciousness fully takes over.
During Gemini of the Meteor, it appears Mao had his consciousness recovered on CIA servers and he now possesses Suou's pet momonga, Pecha. He travels with Hei for the majority of the series, taking on a similar role to season one. Near the end of the series, Madame Oreille addresses him as Ricardo, possibly giving us his real name.
It is later revealed that Mao had met Suou's mother in the past. He paid compliment to her whilst she was pregnant, and then saw her again whilst he was on a mission.
His mission was to discover the secret behind Dr. Pavlichenko's research at a university in Moscow. He infiltrated the university in the body of a black cat. Moments later, the university exploded, obliterating his original human body.