Ruby Moon, along with Spinel Sun, is one of Eriol's henchmen. He created both of them to help him with his magic and for company. If this situation sounds familiar, it is. Coincidentally, (or not...) Ruby Moon and Spinel Sun are a pair similar to Yue and Cerberus. Strikingly familiar, huh?
Ruby Moon's personality is pretty much the same as Nakuru, only she tends to be a bit more serious. Or at least, not as hyper-active. She has pinkish-red hair, and huge black butterfly wings. She uses the magic she got from Eriol to help him cause trouble for Sakura.
Ruby Moon, just like Yue, has
a secret identity! And hers packs
a punch. ^_^ *Spoilers!!*