The cage hangs a little off to the left of her chair. She doesn't need to turn her head much to see it; but neither does Naminé really want to see it. It's kept as a reminder—a constant, menacing reminder.
It's hung like a birdcage, on a long, curved stand, and is made of cool, frosty silver. Innocuously sitting inside is a little doll: an exact replica of Naminé herself. It is here to mock her, to quell her rebelliousness, to trample her hopes.
Naminé is trapped inside this castle as surely as the doll is trapped in the cage; and it reminds her that she will never, ever escape. She is doomed to remain in this room, this whitewashed cell, for as long as she is deemed to be useful. She will never be able to walk freely, to explore the worlds that she draws, to meet the people whose images she conjures.
So when she replaces Kairi with herself in Sora's memories, she feels a little thrill. She can break open her cage's bars and live-albeit vicariously-like a normal girl…for just a little while.
Author's Note: Standard disclaimers apply. I don't own Kingdom Hearts; if I did, I'd sack about half the second game's vocal cast and give Riku more screen time.
I can't quite remember if the birdcage and doll are in the game, but they are present in the manga.
