According to many texts, a nephilim is the child of a male angel, and a mortal woman. This is how the species is to be played here, as a half-angel. While other sources you might find may call them giants, or even Titans, the most commonly accepted description of a nephilim is a half-breed angel. According to the myths surrounding them, nephilims were created when Lucifer and his armies were cast from the heavens, and into the mortal realm. Several of the fallen took for themselves mortal lovers, who bore children for their angelic mates. While this is how the originals came to be, your nephilim does not have to be a child of the fallen. He or she may be the son or daughter of any angel you wish, named or otherwise. It doesn't even have to be based in the Christian mythos if you don't wish it to be. I myself have a nephilim by the name of Sade Ravine, who is the son of Michael, Pagan archangel of fire. A nephilim's abilities are dependant upon which mythos his or her angelic parent is drawn from. If taken from Christian beliefs, a nephilim generally has the basic, holy powers of an angel. If taken from Pagan beliefs, a nephilim will have powers based in whatever element his or her parent was aligned to, be that fire, earth, spirit, ect. A nephilim is, in a way, immortal, as it's body does not age past a certain point. However, agelessness does not, in any way, equate invincibility. A nephilim is much easier to harm than a pure angel, but is also a more dynamic character, as they are not bound by angelic laws. Overall, a very fun species to play, as you can be very creative with your nephilim's origins and abilities.