Appeared in the sidestory in volume 10 and episode 7 of the anime.

Nickel Doll is well-mannered whenever she participates in matches. However, it can change radically whenever the situation worsens for her, making her frustrated and acting almost childish. However, she is able to recompose herself when she becomes serious. She does however dislikes someone if they are to reveal the nature of her tricks and attacks.

(Source: Accel World Wiki)