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 …

The series deals with issues and ideals of virginity, and sexual intercourse in that Chi is effectively incapable of sexual intercourse (in the manga and in the series), as attempting to do so would “reset” her, so she must therefore only entrust her body to someone who cares for her well-being as opposed to a purely sexual relationship.
Freya explicitly tells this to Hideki in the final scene of the manga, that to have Chi, pointing between her legs, means that Chi would lose all her memories. However, earlier in the …

“Watashi” (a first person pronoun in Japanese), a character drawn by Chitose Hibiya in a children’s picture book A City with No People, is used in the series to hint at the definition of reciprocated love to Chi, and is used to highlight issues with human-persocom relationships; drawing upon the fact that because persocoms can be programmed to imitate desirable human behavior, humans would opt-out of human relationships, resulting in obvious problems, such as the inability to further produce offspring.