Kali, the Aethereum Ruborem

After the 'Scissa Mundi' incident, a catastrophe that wiped out one of the biggest cities in the country alongside all of its inhabitants in mere seconds, a company called 'Postridie' managed to obtain the weapon that caused such carnage, the 'Aethereum Ruborem', and sealed it in a faraway secret facility. You've been tasked with discovering how this weapon works. But when you arrive at the facility, instead of a horrible super weapon you find a scared and chained girl, with red eyes and a red hair which emits a soft, ethereal glow.