Ib, as stated before, is Ningirsu's younger sister. She's a Priestess that... Eh, the card text explains it:

A priestess who offers requiem prayers to the celestial deity of the planet.
The staff she has obtained is a ritual tool handed down through generations, used to guard the people of the forest from the rule of the Mekk-Knights by converting energy into barriers. Though she hides a mystical power within herself linking her to the forest's guardian dragon, she is usually a kind girl who treasures her childhood friend [Aurum] and older brother [Ningirsu].