Kazuya receives May, a hand sized 1/6th scale cyberdoll, in a package from Cyberdyne Co. (not to be confused with The Terminator's robotic company, Cyberdyne Systems) because of an accidental order which happened as a result of a revenge tactic planted in a CD from his rival, Nanbara. A cyberdoll, May was never paid for by Kazuya. Cyberdolls can control traffic lights and simple electronics and connect to personal computers via what may or may not be USB cables. She later becomes a human-sized 17-year-old version. Her personality is innocent, and at times childish and naive, though she also shows surprising insight and is always able to cheer Kazuya up. Unlike the other Cyberdolls, May's Maid Program had evolved, making her more human and resistant to the retro-cybervirus that threatened the other Cyberdolls. She shows strong feelings of affection toward Kazuya and is often competing with Kasumi. In the last episode it has also been stated that she can give birth.   (Source: Wikipedia) 

Saotome Kazuya is a computer whiz. One day his friend Nanbara, threatens him with a computer virus. Trying to stop the virus, Kazuya ends up making a special order. May is a cyberdoll that arrives at his door a few minutes later and she is 1/6th the size of a normal person, which makes for many awkward situations. Not to mention the fact Kazuya can't even afford to keep May. Cyberdyne is not satisfied with Kazuya's non-payments and will do anything to retrieve CBD May.
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(Source: Anime News Network)

At Kazuya's apartment, a package from Cyberdoll Mami filled with five "Chibi-Cyberdoll Mays" arrives. Later, an accident causes May's personality to go into the five mini-May's, each one receiving a distinct aspect of her personality. Elsewhere, Rena finds a lost child and brings it home.