It seems that the ending to Chobits, and the whole story behind it confuses some people. It's really not -that- complicated, but I'll try to explain the whole thing here anyway. However, this contains just about every spoiler in the series, so please don't read this if you haven't finished the manga/anime. Also, I'll be going mainly off the manga here, since I have that readily avalible.
The idea for the creation of a "Chobit" first began a long time ago when Chitose and Hibiya and Mihara Ichirou were first married. They had both worked together as part of the scientist team that created the first batch of persocons. These persocons were then sold to a client orangization. It was at this time Zima and Dita were first created as well. Zima was created first as a log of all persocons in the world, and to store all their data, and then Dita was created as his protector, as a kind of firewall.
Anyway, soon after Hibiya and Ichirou were married, they realized that Hibiya couldn't have children. So, as a present to his wife, Ichirou started work on a special line of persocons, so he could make one to give to his wife. The special thing about this persocons were their operating system first of all, that acted just like a child's: it was blank at first, but then as the persocon had experiences they were able to learn and grow like a baby does. Also, installed in this special series of Persocons was a program that gave them the ability to find one person, whom they would love.
The first one of this line was called, Freya, and became Hibiya and Ichirou's daughter. She grew with them, and soon found the person just for her. Unfortunately, it was Ichirou, but her parents had not realized it yet. They noticed she was sad so they decided to make her a sister, called Elda. At this time, the special line of persocons became known as "Chobittsu" or Chobits. Ichirou was the one who named them, because they was two of them and they were small and cute, but he really got the name because it was all letter's from Hibiya's name.
Freya, Elda, and their parents formed a happy little family, but Freya could still not get over her romantic love for her father. Soon she started to disapear the heartbreak was so bad. One day she happened to catch Ichirou by himself and confessed her feelings, but he was forced to turn her down because he loved his wife the most. Just as Freya was about to dissapear for existance completely, Elda came and told her that she would absorb her memories and personality. This would erase all of Elda's info, but she thought that Freya's memories were more important, and anything Elda had worth remembering Freya remembered too.
Just as Elda finished absorbing the last of Freya's memories her parents ran in. They realized what was happening, but could do nothing about it. Just before Elda completely lost herself, she asked her parents to put her somewhere far away, where she wouldn't see them, so she could find her special person on her own and not suffer the same fate as Freya. Hibiya placed all her memories on a disk, and put her in the garbage dump outside the apartment. She watched for a long time as people came by, almost taking Elda, but then choosing not to because her OS seemed blank. Sometime during this time, Hibiya's husband passed away from an illness.
Eventually Hideki came along and took Elda home with him, where he renamed her Chii and started to teach her things about life and love. The character "Dark Chii" is really just Freya's memory inside of Elda, helping and guiding her and hoping that Chii can find her true love. The series progresses through all their adventures until Dita and Zima show up again. Apparently, before Elda/Chii was placed in the trash dump, Ichirou installed a special program on her. The two persocons do not know what the program is, but they know it will be disastorous for persocons everywhere if it goes into effect.
Zima tries to hide the fact that he knows where Chii is all along, but Dita ends up hacking into him and finding out herself. Hellbent on destroying Chii, she heads to Hideki's apartment, right after Chii confesses her love for Hideki, and Hibiya explains her and Chii's past to him. Dita tries to shut down Chii quickly, but is deflected. It is now up to Hideki to make up his mind about how he feels about Chii, as water spreads throughout the city, and every persocon remains in a trance.
As soon as Hideki realizes he DOES love Chii, the world starts to return to normal. Except that when the persocons come out of their trance, they have a new emotion. It turns out that the program that was installed in Chii had a chance of going two ways. If Chii did not find the person just for her, the program would have been negative and destroyed every persocon on the plantet. This safeguard was put in by Hibiya and Ichirou because they felt that all persocons were their children, and if their daughter couldn't be happy there would be no point for the rest of them. However, since Hideki did accept Chii as the one he loved, the program went in the oposite direction and awakened the ability to find true love for every persocon on the Earth.
This is pretty much what I can gather about the origin and purpose of Chobits from reading the ending of the series. Sorry if it's a little wordy, and if you see something here that you dont' agree with, please email me to discuss it. :D
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