Sivil is first seen on the battlefield, wiping out entire squadrons of variable fighters in a single blow. She becomes greatly interested in Basara Nekki due to his powerful Anima Spiritia, a potent sound energy that drives her into a frenzy.
Basara himself becomes intrigued by her, and hopes the power of his song will be enough to turn her away from evil. This sparks a rivalry between Basara and Gigile, one that would see the latter realizing the error of his ways, and sacrificing himself for the greater good. Sivil herself falls under a deep sleeping state, and is awoken towards the end of the series. She too realizes the error of her ways, and fights against the Protodeviln.