When computers start to look like humans, can love remain the same? Hideki Motosuwa is a young country boy who is studying hard to get into college. Coming from a poor background, he can barely afford the expenses, let alone the newest fad: Persocoms, personal computers that look exactly like human beings. One evening while walking home, he finds an abandoned Persocom. After taking her home and managing to activate her, she seems to be defective, as she can only say one word, "Chii," which eventually becomes her name. Unlike other Persocoms, however, Chii cannot download information onto her hard drive, so Hideki decides to teach her about the world the old-fashioned way, while studying for his college entrance exams at the same time. Along with his friends, Hideki tries to unravel the mystery of Chii, who may be a "Chobit," an urban legend about special units that have real human emotions and thoughts, and love toward their owner. But can romance flourish between a Persocom and a human?

Meg, faithful and gentle, Jo, independent and energetic, Beth, quiet and shy, Amy, amiable and precocious–the four sisters live vigorously and happily at home with their gentle mother while waiting for their father to return from the Civil War. Helping each other, they challenge their fates and grow up to become wonderful women.

A normal looking high school girl on the outside, Kusakabe Maron is actually the reincarnation of Jeanne d' Arc. With the help of the angel, Fin Fish, Maron works as the thief Jeanne at night to seal the demons that reside in pieces of artwork, preying upon the weak hearts of the owners. She is branded as a thief due to the fact that the artworks disappear after she seals the demons. One day, a new neighbor and classmate appears, as well as a rival in her night job, the thief Sinbad. With her own best friend being the detective's daughter, out to capture her and the appearance of her new rival, Maron's work is anything but easy.

Masahiro Setagawa is a hopeless teenager who is often used by the neighborhood bullies as an errand boy. Defenseless, Masahiro knows that nobody will ever save him. However, his life drastically changes when he meets Kousuke Ooshiba, a man known as the "Bear Killer," who takes down neighborhood gangs. A year later, Masahiro and his former friend, Kensuke Ooshiba, attend high school, only to find that Kousuke is their math teacher. While the three grow closer, Masahiro starts to view Kousuke as his "hero," and Kousuke develops an urging desire to protect Masahiro. However, their normal lives take a turn when Kensuke's childhood friend, Asaya Hasekura, returns, seeing Kensuke as more than just a friend, much to his surprise. Will the three boys be able to live a regular high school life? Or will forbidden love keep them apart forever?