Shalott is one of the 58 gravity children onboard the aircraft carrier and is also one of the six kings.
A lolita in appearance, depicted wearing a long elegant dress and bonnet, one would obviously think Shalott's a girl. In actuality, however "she" is a man.
He works with Arthur, another one of the 58 gravity children, using his mirrors to reflect any damage Arthur receives back at the enemy. He has some special mechanisms in his ATs that allows him to create these mirrors.