A robotic schoolgirl that was built by a Professor. She often worries about keeping her identity as a robot from others, despite the fact everyone already knows about it due to the noticeable wind-up key exposed on her back. Luckily most don't make a big fuss about it. Her limbs will sometimes fall apart, revealing dubious items that Professor has installed without her noticing, ranging from bean-firing-weapons to Swiss rolls. She is also the Professor's caretaker. She wishes to live life as a normal girl and therefore really wants the wind-up key on her back removed.
In the last episode, after her school friends come over for a surprise birthday party, Nano decides that although the key has been annoying, she prefers things the way they are. The Professor installs a new key on her back that looks the same but spins when Nano is happy.