Ruby is Meimi's pet Hedgehog. Her manga introduction is half way through the story, while her anime appearance is quite early in the series. She was bought by a man who forced her to swallow a gem. Saint Tail then steals Ruby from the man to protect the gem inside of her. Ruby also knows Meimi is Saint Tail, and has even been on a previous caper with her, although Meimi has to keep Ruby hidden from Asuka Jr. so he won't recognize her from the previous caper she was in.