The Heavens:

This is the code name originally given to the external web surrounding the Earth, commonly referred to as the "sky." Its primary function is to capture souls which leave the bodies of the deceased and float upward. The spirits decorating the web create the lights during the night which are known as "stars." The moon, which is thought to be a mass of rock revolving around the Earth, actually happens to be eye of the filter, its real name being unknown to Humans, although it is the location which their myths refer to as "Heaven," an area where a congregation of spirits govern the Earth and the web which surrounds it. This group constantly shifts, as they give up their eternal existence in order to live once again, eventually expending the energy contained within their souls and fading from reality altogether. Frequently these powerful beings have appeared before humans, being recognized as aliens, gods, angels, demons, and other ethereal beings. On occasion, souls become detached from the web and revolve around the Earth, being seen as shooting stars, comets, or meteorites. Some of these souls will reattach to the web, while others make their way to the surface of the globe, and walk the planet again as eternal "ghosts."
(I'm sorry, it's a very short explanation, more to come later.)

Stella:

A specific soul which fell to Earth. She is apparently in the "nebula" stage of a soul's existence, as it goes through specific stages, some aging faster than others. Unfortunately, every light fades eventually, but their existence does happen to be ridiculously long. Most would consider it very boring.
This soul, after being shaken free from the filter which kept it from passing outside of the Earth's "universe," crash-landed, and became free to walk the Earth once again. A very special case, she collided with a passing divine governor and possessed its body. When she descended, she held a body not only capable of being completely recognized as human, but also holding an intense power allowing her to control the fire-like energy known as her own soul. She loves to kill, and sees it as almost a game. Terror envelops those who cross her path.
Her constant use of the fuel that she draws from her spirit is very exhausting and threatens to end her existence constantly, and so she not only slaughters others, but devours their souls to keep herself alive.
(Once again, it's rather incomplete.)