Life energy is gained from life. But most of life on earth are dead so they give off life energy. Life energy is basically their life force. What powers them. Life Energy gives you the power to do miracles like restore life in sections of the game.
Life Skill 1: Void Drain
This skill is really good against Void Beasts. It closes Void Portals and recycles it into Health Points. It also can get rid of excess void energy.