キャスター

The servant of Alice. Aside from the color of their clothing, they are identical in appearance. She cares for Alice a lot.

Her true identity is Nursery Rhyme, which isn't really considered a hero. She is based on Lewis Carroll's book, Alice in Wonderland, which was originally a nursery rhyme.
She herself is a Reality Marble, projecting the heart of her master and creating a pseudo-servant. Her Noble Phantasm is called The Queen's Glass Game.