WARNING! Semi-spoiler!

Anime in which Mima Tokiko, usually just called "Key", is a little girl who thinks she's a robot, as a result of certain experiments her grandfather performed on her when she was quite young. Her grandfather is now dead, leaving her with instructions to make 30,000 friends in order to become "human."
The premise of the series sounds goofy, but it's actually very good and ends up not being at all what you'd expect.