The story centers on the life of Hideki Motosuwa, a repeat student (浪人, Rōnin?) attempting to qualify for university by studying at the Seki prep school in Tokyo. Besides a girlfriend, the other thing he dreams of having is a Persocom. A Persocom is an android used as a personal computer; however, they are expensive, and Hideki has no money.
On his way home one evening, he stumbles across a Persocom in the form of a beautiful girl with long blonde hair lying against a pile of trash bags. He first thinks this to be a murder but, realizing she was a Persocom, he carries her home. Upon turning it on, she instantly regards Hideki with adoration. The only word she seems capable of saying is "chi", and thus he names her Chi. Although Chi does not appear to have any programs installed in her, Hideki's friends surmise that she must have some sort of learning program installed, judging from her behaviour.
A major part of the plot involves Hideki attempting to teach Chi words, concepts, and appropriate behaviours, in between cram school and work. At the same time, Chi seems to be developing feelings for Hideki, at an emotional depth, which Persocoms are not supposed to possess, and Hideki struggles with his feelings for her. The series explores the nature of Persocoms, human interactions with them, and the nature of love. All sorts of characters and their Persocoms are introduced, some of them loving Persocoms, and some of them considering them only as tools, and some of them hating them altogether.
In the later part of the story, the characters start to explore Chi's mysterious past. Chi discovers a series of picture books of mysterious origin, that seem to awaken something deep inside of her. The book inspires her to find the "person just for me", a euphemism used in the series to refer to one's true love. Chi is also a very special Persocom, and towards the end of the story, together with Hideki, discovers her true identity, as well as what lies within her.
