Rei is a good robot. He is obedient and calm, thoughtful, polite. He wants to fulfill his purpose.
Yet he is curious about all sort of things and underneath it all he has courage and determination of his own. And he may yet find a different purpose for himself than the one he knows of.
I changed Rei's face-up for the sake of giving him a slightly different expression, it's a lso a tiny bit less girlish, I think.