"C.C.~! I'm waiting for you!"
He was found by the Grey Witch; an orphaned Chinese boy of six, alone and uncared for. In hopes that the boy would some day be able to fulfill her wish, C.C. made a contract with him at that young age, bestowing upon him the power of the Geass. The abilities of the Geass varied by those who were gifted, and in the case of Mao, the young boy gained the power to hear the thoughts of the people around him. Unfortunately for him, this particular power quickly reached the point where it could not be turned off, subjecting him constantly to hearing the minds of all those around him.
The incessant thoughts that poured into his mind began to take a toll on Mao's sanity. For him, C.C. was his only solace, his sanctuary. When his powers became overwhelming, she helped him to focus. Being that she was the only person whose thoughts could not penetrate his, her presence was a great comfort to him. She was his guardian, his lover, his world. He would have been content to remain with her for the rest of his days, but C.C. had begun to see that her wish would never be fulfilled at Mao's hands. She left one day, never thinking that Mao would ever break his isolation and step into the noisy world to find her.
Though the details were lacking in what happened between then and when he appeared again to stalk C.C.'s new contractor Lelouch, it was obvious C.C.'s surprise in seeing that Mao was still alive. Still clinging to his longing for the Grey Witch, Mao confronted Lelouch Lamperouge, proving a challenge for someone who relied so much on his wit. He very nearly got Lelouch's close friend Shirley to kill the black-haired student by reading her thoughts and twisting them upon her guilt. Mao failed to get things to work out as he planned, but he was able to see C.C. once again, making him eager to be reunited with her. The existence of another Geass user came as a shock to Lelouch, and it led him to question C.C.'s loyalty to him. He prepared himself to face Mao, worried that the young man would expose his secret as Zero. C.C. assured Lelouch that Mao had only interests in her, and when he contacted Lelouch to speak to C.C., she left to meet Mao, claiming she would deal with things herself. Lelouch tracked them down to an empty amusement park where Mao had begun to exhibit his waning grasp on sanity as he threatened to cut up the green-haired immortal with a chainsaw, claiming it would be the easiest way to transport her on an airplane to their new house in Australia via luggage. Lelouch managed to outsmart him once he learned of Mao's limitations. The local law enforcement had been called in to deal with a suspected kidnapper on the Refrain drug, and using them as a diversion, Lelouch came to C.C.'s rescue while Mao was shot repeatedly and left for dead.
This was not the case as Mao once again surfaced, this time on the campus of Lelouch's school. While he had not been unscathed by taking multiple wounds, he claimed that Brittainian medicine did wonders to help him recuperate so quickly. Kidnapping Lelouch's younger sister Nunnally, Mao baited Lelouch to come and meet with him again. Suzaku sensed that Lelouch was acting strangely around the school grounds as he was searching for his sister's whereabouts and eventually ended up assisting him in rescuing Nunnally while Lelouch went to meet with Mao. Using the Geass on himself, Lelouch tricked Mao long enough to distract him so that Suzaku could disarm the bomb that had been left with Nunnally. Suzaku then came to join Lelouch to take Mao down, but in his desperation to gain ground over them again, Mao sifted through Suzaku's mind instead, revealing the truth of his father's death. Angered at Mao for the distress he was causing, Lelouch found an opening and used the Geass, commanding him to "shut up." Finding himself unable to speak, Mao made to retreat, and C.C. was waiting for him outside. Overjoyed to see her again, he didn't notice the regretful expression in her eyes, but her words hit him only seconds before she pulled the trigger on the silencer, shooting him in the neck: "Wait for me in the next life, Mao."
Mao's abilities with the Geass have not helped for his mental stability. Being able to hear everyone's thoughts and incapable of doing anything to shut it out, he had lived in isolation for most of his life. His contact with people has been very limited. Having lost his parents early on, he lived without the influence or experience of having a loving family, nor had he proper upbringing in education. C.C. became a great influence to him, and he naturally developed an attachment to her since she was the only one who seemed to care for him. She promised to stay with him, she was the only one who was immune to his ability, the only one whose thoughts he could not hear. To help him keep his focus away from the intrusive thoughts of others, Mao wears a headset that's on constant repeat with words from the woman- words of encouragement and caring. He believed himself in love with her, although it wasn't as deeply shared. His aspect of love became distorted, and he became very possessive of her to the point that he would go to any lengths to get her back.
His social skills are undeveloped, but he's managed to overcome the anxiety at becoming overwhelmed by the idle thoughts of the people around him in order to try and make things the way he wants them to be. He doesn't seem the type for random conversation, and if there is no reason to deal with people, Mao will gladly avoid the trouble. Most of the time, the only reason he will speak to others is to get something he wants. Undeniably he's learned quite a bit about the world, he's learned how to manipulate people by listening to their thoughts and using the right verbal prods. Otherwise he sees most people as annoying and careless, wasting their minds on meaningless things, and it aggravates him to have to hear it all.
Although seventeen, he has a very juvenile air to his actions and the way he thinks. He's easily entertained when things go as he expects them to, clapping his hands in what might appear to be a childish manner. His reasoning might be twisted, but his views are simplistic. If things don't go his way then he'll become disappointed, but that won't keep him from trying to fix that. If he can't get people to cooperate with him, he'll just do it by himself.Violence seems to be a quick fix for a lot of things! His methods for dealing with things might seem a little extreme though. Mao's prone to throwing tantrums if he's pushed too far, and if he's armed with a chainsaw then it's wise to be a good distance away from him.
It isn't completely his fault that he's a bit of a recluse and a sociopath. It might take some patience to deal with him, but he can be reasoned with. All he really wants is to enjoy a peaceful life, after all.
Having been gifted with the Geass by C.C. when he was six, Mao is unable to control his power, that of which is the ability to hear the thoughts of others. This is unfiltered and has a radius of 500 meters. This proves as much of a disadvantage to him as an advantage because he has no way of shutting out random thoughts of anyone within his vicinity. In order to try blotting out those thoughts if he cannot avoid people, he wears a set of headphones that replay various voice clips from C.C.
Although he can't turn off this power, he can focus it on a person and delve through their innermost thoughts. If he concentrates, he can even penetrate the unconscious mind. It's by this method he's able to manipulate a person mentally if he so wishes, sifting through their guilts and phrasing his words to disturb them into desperate action.