FANTASY ACADEMY
An angel, lost on Earth after failing to return to heaven, reincarnated as a human but retained his celestial powers. As he aged, the power became too much for his mortal body, leaving him lonely despite having siblings. He eventually made a close friend and, knowing his time was short, began distributing his powers through injections of his celestial blood. His friend was the first to receive powers, followed by the angel's sister and many others.
To help these new power-bearers, the angel created a separate universe above Earth with a school where they could learn to harness their celestial aura. The angel ruled the school until his friend, seeking control, demanded a share. When the angel refused, the friend took over during his absence, ruling with an iron fist and sparking a deadly war.
The angel returned to find his friend had married his sister, and they had a daughter. Heartbroken, the angel banished them and their followers to a sealed realm called Terra Firma.
Before departing on another journey, he appointed twelve powerful beings to govern his universe and placed his niece and her descendants in charge of the school. Then, the angel disappeared, leaving his legacy behind.