Mao is a minor villain in the first season of the anime series, Code Geass. He is a Chinese orphan who was given the power of Geass by C.C.. His Geass manifests in the form of mind-reading.
Eventually, his Geass went out of control and drove him insane. C.C. promised to stay with him always, as she was the only one whose mind he couldn't read. However, she eventually left him as he was unable to fulfill his side of the contract.
Throughout his brief screen-time, his primary motivation is to make C.C. admit that she loves him and take him back. Because of this, he is a rare example of a male yandere.
He is voiced by Takeshi Kusao in the Japanese version and Ezra Weisz in the English version.
Personality
At first glance, Mao seems a little off, from there on its topsy turvy all the way through the numerous layers of madness. He is extremely sadistic, merciless, and despiteful, relishing the anguish he causes Lelouch when he threatens to blow up his sister and also when he shoots C.C. multiple times in Clovisland.
Though able to keep up a somewhat reasonable persona in the open he obviously does not belong in crowds, his giddy mannerism and emotionally immature personality coupled with zero empathy makes him dangerously unpredictable. As with Lelouch, he has his own opinion on how the world should be, a wide open wasteland with no one in it, other than him and C.C.
Abilities
Physical
Mao is surprisingly strong despite his little frame, though like Lelouch, he is obviously ill suited for physical activity. He makes up for this by being an excellent shot which is shown during his showdown with C.C in Clovisland, shooting the gun pointed at him out of her hand before she can pull the trigger. He is also extremely resilient, able to survive multiple shots by several police officers (though he credited his recovery to Britannian medical science).
Geass
Mao's Geass power allows him to read the minds of anyone within a spherical range of 500 meters (radius) x 300 meters (height), either all at once or from a specific individual if he concentrates, though his range is reduced when he focuses on a single target. Mao's Geass differs from Lelouch's on several key areas but both allows control of other individuals. Mao controls people by reading their darkest and most inner thoughts, then using them to manipulate the person. This is shown through his manipulation of Shirley. However, because his Geass ability can't be turned off, he often struggles to think for himself unless he listens to his recording of C.C..