Nyx

Nyx is the goddess of Night and the aunt of Alisa and sister of Hemera.

History (Not Greek accurate)
Nyx tried to defeat Chaos and his army, but failed when her Niece and sister got kidnapped, when Alisa bacame a guardian, she taught her how to control night clouds and winds. She and Zeus teamed up to start their 200 year army. Which left Alisa to join the guardians in America.