Deriving Chirna

Lore
An equation formed within Chirna's mind, and a mounting sense of foreboding urged her to write it down at once using whatever was at hand. "According to these calculations, the sky is going to fall!" But none of the other townsfolk could grasp the intricacies of her formulae, so her warning went unheeded.

Acquisition
Ranking Reward and Token Box UR in the Battle Royale LVII.

Name origin
?