Chii is a Persocom who is found by Hideki Motosuwa in a garbage dump. At first, she is only able to say "Chii", thus earning her that name. Later on, she is taught various things, and is eventually able to communicate with other people.
She is a Chobit, a legendary Persocom that is capable of thinking independently and feeling human emotions. Her real name is Elda and she has a "sister" named Freya, who died.