Perhaps this is how it begins:
She lives in a cell. She was born in a cell (well: she was born in a petri dish in a cell) and her entire world is comprehended by Floor Three of the lab complex. There may be a world beyond the white walls, to which the scientists in white lab coats retreat every evening and from which they emerge every morning, but Nimona has never seen it.
All she knows is white walls and running through a set of routines: the routine of the various physical tests, the routine of their demanding that she morph into a variety of different creatures while they take notes and readings, the routine of them closing her up at night. She knows what to expect when they walk into the room with heart scanners and she knows what to expect when they walk in with plate armor on. They exclaim every time she does something new, morphs into something bigger or stronger or faster, but she knows the praise isn’t really for her: it’s about her, sure, but it’s directed at the scientists who created her in the first place.
One day, she decides, she’s going to see more of the world. This isn’t a home, not really: it’s a place she’s being kept, but she’s not going to stay much longer. There hasn’t been a prison ever built that could contain her. The human beings who made her just don’t know it yet.
Let’s tell a different story:
She lives in a village. She was born into a family that loves her very much, and she only dreams some nights about a sterile laboratory and it’s just a nightmare, like falling off a cliff or being chased by a clown or something stupid like that. She doesn’t even remember it during the day.
She has friends among the village children. Even if a lot of the other kids think she’s a bit weird – even if they think her thing for sharks is a little strange or her love for pyrotechnics has a tendency to get others in trouble – she has friends: a best friend, the kind of friend any young girl needs, and a gang to play with in the afternoons. She and her best friend fight exactly the way you’re supposed to when you’re eight and make up every couple days over the stupidest things and learn how to French braid by practicing on each other’s hair and talk about how they’re going to go be adventuring Knight-Princess-scuba divers someday together.
There are raiders sometimes, yes; but she has a mother who laughs at her jokes and a father who is twice as tall as she is and lifts her up sometimes so her head brushes against the roof, and so raiders don’t matter that much. She knows where the trick floorboards that creak are and where the nearest hidden hollow is in the forest beyond their house, and running into the woods and crouching down low behind the trees is just as much a part of being at home as wood smoke and the smell of her father’s cooking are.
She lives in a castle. But before that, she lived in a cave, and the castle is new to her and confusing. She’s trying this human thing for the first time, and everyone, of course, expects her to have it down pat because they don’t know she’s really Nimona. (Of course, she’s not even entirely sure what “really Nimona” means anymore.) She’s learning to be at home in this new human body just the same as she’s learning to be at home in a castle.
Living in a castle is very, very different from living in a cave. She has a massive room and an enormous bed with fluffy pillows and thick sheets. She has a weapons collection and she's supposed to know what the names of each of these cruel, shiny lines of metal are and how to use them. Over the centuries, knights have attacked her with enough of them that she certainly recognizes the swords and maces and morningstars and so forth, but it's a novelty to actually hold them herself. She trips over her own sword the first time she tries to swing it and has to pretend that fighting "the monster" left her with a concussion.
People are always bustling around the castle, but they actually like her - whenever they see her, they pause and smile and greet her respectfully. No one cries or screams or attacks her. And if the name they use is "Gloreth" and not Nimona, well, that doesn't really matter so much, does it? Maybe she can shapeshift names just the same way she can shapeshift bodies.
But the stone walls of the castle aren't much different from the stone walls of the cave. And Nimona didn't decide to leave her cave just so she could lie low in a different lair. Maybe it'll be time to move on from this home too, sometime soon.
She tells herself stories about who she is. Well – she tells other people stories about who she is, but sometimes she wonders whether her audience isn’t really just herself. Sometimes she was a young girl in a village besieged by raiders, who learned to shapeshift to save her family. But other times she was a squirrel who learned to turn herself into human shape, or an old woman who was given the gift of infinite variation in appearance for her kindness, or a wizard who learned to shapeshift after selling his own soul to a monster. (Sometimes, she’s the monster.)
Most of the time, she lets people come up with whatever stories they want – it’s kind of easier that way, and it’s funny to hear what they think she is. She’s been a crone and a cursed maiden, a dragon, a poltergeist, a unicorn turned evil, and, once, a mermaid. (She’s not entirely sure how that one worked – apparently, some villagers had developed a theory that she was wheeled around in a massive glass tank and her changes in appearance were just the result of “refraction,” which, as everyone knew, was complicated and science-y and difficult to explain, but could definitely make someone look like everything from a wolf to a dragon to a human being.)
She sets herself little goals, because if she didn’t have anything to achieve, where would the fun in that be? Of course, most things are easy to do as a shapeshifter, but that’s besides the point. One time, she challenges herself to enter a tournament as eight different knights and make the quarterfinals as all of them, and then disappear mysteriously into the ether. Another time, she tries to steal every single left shoe in an entire village, and then she hides as a mouse in the grass to watch the humans hop around in confusion. One rainy day, she even tries to learn how to knit.
She hears about Ballister Blackheart while she’s trying to steal enough wanted posters from the local guard station to make a collage. She takes his poster because his goatee looks cool (she tries it on her own face, but decides she’s not a fan of how it looks in red and is too attached to red hair to go brunette), and then she realizes that his bounty is way higher than anyone else’s. Which seems cool, so she decides to stick around the Kingdom for a while and find out more about this guy who seems to have the whole kingdom living in fear of his (evil) ways.
On a whim, she decides she wants to meet him. Maybe get to know him. Anyone that inventive who can command that much respect must be interesting – and she’s bored and in need of a new self-set goal anyways. Perhaps finding out how Ballister Blackheart works can be her newest quest.
So she sneaks into his castle as a beetle in the dead of night and then gets distracted by the cool bubbly fizzing things in his lab and wanders around until the man himself comes in the next morning and demands to know who she is.
She decides that here, she will be a sidekick. Later on, she will decide to be a shapeshifter, but she doesn’t know that yet.