A major part of the plot involves Hideki attempting to teach Chi words, concepts, and appropriate behaviours, in between his crammed schedule of school and work. At the same time, Chi seems to be developing feelings for Hideki, at an emotional depth, which she is not supposed to possess, and Hideki struggles with his feelings for her. The need to figure out more about Chi and her mysterious functions and past becomes a stressing pull for the characters in the series.

Hideki discovers that his feelings intensify for Chi whether she is a persocom or not, despite other horrible experiences involving persocoms that happened to his friends. Chi becomes aware of her purpose through a picture book series called A City with No People which she finds in a bookstore.
The books speak about many different things involving human and persocom relationships: persocoms and their convenience towards people as friends and lovers, how there are things that they cannot do and questioning whether a relationship between a persocom and a human is …

As the series progresses, Chi begins to have visions of another persocom who is identical to herself, and eventually learns this is Freya, her twin, and that Chi was originally called Elda; after Freya fell in love with her father and creator and had her heart broken (she couldn’t muster the courage to admit her feelings in the anime), her memories were downloaded into Chi, before her system was wiped at her own request.