A Soul is by definition a stream of energy that can evolve on it's own. These energies are often visible as thin clouds through the Ethereal in various colors. Despite of having different colors, souls have no visible identification of it's predestined individuality. There are two ways a soul can evolve without outside help. Either the soul is coming in contact with an energy that streams through the Universe, shaping a Spirit, or it forms a mold around itself, shaping a Being. In both ways, the Soul can gain more energy and become stronger. Souls spawn throughout the Ethereal and in other layers of the Universe, though quickly die off and leave elemental remains when exposed to other worlds.
For other Beings or Spirits, Souls can be a source of energy, since they can be devoured or absorbed. This releases the Soul's energy directly into the Soul of the predator.