Mao

Mao (毛) was a Chinese orphan who at the age of six was given the power of Geass by C.C.. His Geass power allows him to read the minds of anyone within a 500 meter radius and 300 meter high, either all at once or from a specific individual if he concentrates, though his range is reduced when he focuses on a single target. His Geass, like Lelouch's, eventually became permanently active, and the constant influx of thoughts from all around him drove him insane. C.C. states she abandoned him because he was not able to fulfill his part of their contract. C.C. never explained what her contract with him was and so it can be assumed that it was the same as Lelouch's, which was for him to kill her. Because he loved her, Mao was incapable of killing C.C. In order to compensate for his uncontrolled power, Mao wears sunglasses to disguise his eyes and headphones which repeatedly play recorded words of encouragement and gratitude from C.C. in order to block out the thoughts around him.

Mao's Geass made him an outcast, so C.C., being the only person whose mind he couldn't read, kept him company. As a result of his lack of human contact, Mao is a fairly childish person, a fact only amplified by his insanity. He refuses to accept that C.C. doesn't love him, and pursues her relentlessly. Mao's mind-reading Geass makes him adept at playing on the insecurities of others to manipulate them. He has a habit of clapping when talking to others, often for no apparent reason which only further signifies his insanity.

When Mao finally finds C.C. in Area 11, she tries to get rid of him after Lelouch muses that killing him would have been more humane. However, she fails and Lelouch ends up rescuing her, using his Geass to make the local law enforcement shoot Mao. Unfortunately, since Lelouch ordered the police to "shoot" instead of "kill", Mao survives with the help of Britannia's advances in medicine. He then kidnaps and holds Nunnally hostage in the lower levels of the Ashford Academy, hoping to lure out and eliminate Lelouch in an elaborate game. Lelouch and Suzaku collaborate and succeed in rescuing Nunnally and defeating Mao, but the latter reads Suzaku's mind, revealing the true fate of his father. Lelouch silences Mao with his Geass, and as Mao tries to escape, C.C. appears and tells him that she did love him (as Mao could not speak at the time his facial expression would imply joy at this) and then tells him to wait for her in C's world, she then kills him with a silenced pistol to the neck.

Personality & Quirks
At first glance Mao seems a little off, from there on its topsy turvy all the way through the numerous layers of madness. 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 other persons than him and C.C.

Physical
Surprisingly strong despite his lithe frame, though like Lelouch he is obviously ill suited for physical activity. He is also extremely resilient, able to survive being shot simultaneously by several police officers. (though he credited his recovery to Britannian medical science)

Geass
Mao's Geass differs from Lelouch's on several key areas but both allows control of other individuals, through his version Mao can literally read minds. Although this leaves him quite unable to think.