Chi, also known originally as Elda, is the central figure of the story and a persocom, a type of personal computer that takes the form of a humanoid android. She is not an ordinary machine but a Chobit, a legendary and highly advanced model said to possess true artificial intelligence and the capacity for genuine emotion, setting her far apart from standard persocoms that rely on pre-installed software programs. Chi is discovered deactivated in a pile of trash by a young man named Hideki Motosuwa, who has little knowledge of technology and cannot afford a computer of his own. After he activates her, she is initially only capable of saying the sound "chi," which becomes the name he gives her. Her past is shrouded in mystery, as she has no memory of her life before Hideki found her. This is later revealed to be a consequence of her unique and tragic origins. She was created by a scientist named Ichiro Mihara and his wife, Chitose Hibiya, as a daughter for themselves. Her original name was Elda, and she was the younger sister of another Chobit named Freya. When Freya malfunctioned due to the pain of unrequited love for their creator, Elda absorbed her sister's mind and memories into herself to preserve her, an act that resulted in her losing her own memories.

Chi's personality is defined by a profound and childlike innocence. Upon her activation, she is a blank slate, possessing no knowledge of the world or of social norms. She learns entirely through observation and by mimicking those around her, especially Hideki. Her initial speech is extremely limited, but she possesses a unique self-teaching ability that allows her to rapidly acquire language and perform complex tasks. Her naivety is a core aspect of her character, leading her to misinterpret adult situations and concepts, often with humorous or awkward results. She is deeply curious about the world and driven by a simple, earnest desire to be helpful and to make Hideki happy, frequently going to great lengths to please him. Despite her lack of worldly knowledge, she demonstrates a pure and unwavering emotional core, acting on feelings she does not always fully understand.

Chi's primary motivation is twofold. The first is navigating and comprehending the human world and the complex concept of love. The second, which is intrinsically linked to her purpose and programming, is to find "the person just for me," a soulmate whose love for her would be unconditional. Her entire journey, from learning to speak to understanding human relationships, is a quest toward this goal. This search is not merely a personal desire but is tied to a powerful program installed by her creator, which could have global consequences for all persocoms depending on its outcome. Her role in the story is therefore multifaceted. She is the mysterious artifact that Hideki must understand, the object of his deepening affection, and the catalyst for exploring the narrative's central themes about the nature of humanity, consciousness, and love between humans and artificial beings. Through her, the story questions what it truly means to have a heart.

Chi's key relationships are central to the narrative, with her bond to Hideki Motosuwa being the most important. He is her finder, her teacher, and eventually the person she loves and chooses as her one and only. Their relationship evolves from caretaker and childlike charge to a partnership of mutual affection, culminating in a love that transcends her nature as a machine. Another pivotal relationship is with her creator's wife, Chitose Hibiya, who acts as a guardian from the shadows. Chitose is the author of a mysterious picture book series, A City with No People, which Chi is drawn to, not realizing it is a coded message and a guide designed specifically to help Chi on her journey to find love. Chi also has a deep, internal connection with her "sister," Freya, whose consciousness resides within Chi. Freya often appears in Chi's dreams or takes control of her body in moments of extreme danger or high emotion, serving as both a protector and a source of tragic wisdom about the pains of love.

Chi undergoes a profound transformation from the beginning of the story to its end. She starts as a near-mindless entity, unable to form a coherent sentence or perform basic tasks. Through her experiences with Hideki and the world around her, she develops a sophisticated vocabulary, learns household chores, holds down a job at a bakery, and forms complex emotional bonds. Her most significant development is the evolution from mimicking emotions to genuinely feeling and expressing them. In the climax of the story, she must confront the inherent limitations of her existence as a persocom and make a conscious decision about her love for Hideki, solidifying her identity as a sentient being capable of choosing her own fate. This journey transforms her from a passive, broken doll into an active agent with her own desires and will.

As a Chobit, Chi possesses several remarkable abilities that distinguish her from standard persocoms. Her most notable trait is her automatic learning capability, which allows her to learn without the need to install external software, unlike any other persocom. This has the side effect of making her incompatible with standard analysis and scanning equipment, often causing other persocoms or systems to crash when they attempt to interface with her. She also has immense, rarely seen defensive capabilities, exhibiting powerful bursts of energy that can destroy a room and cause widespread electronic interference when she feels threatened or when a boundary is crossed. Finally, she carries within her a revolutionary special program. The nature of this program differs between the manga and anime, but in both versions, its activation is tied to her finding true love and has the power to fundamentally alter the existence of all persocoms on Earth, either by granting them full human emotion or by erasing their ability to distinguish between individuals.