His story is that he was the second in charge of a local criminal gang, at least until a murder and an insurrection from a particularly nasty individual prompted a inexplicable change of heart in Joel, and opened his mind and body to his powers.

The powers were designed. Because folks have different ideas about how Angels are supposed to be, including their weird powers, the manifestation of Halos in this guy's moveset is a testament to that mindset which I guess is supposed to be an intentional mockery. Nephs would be treated as being no different from X-Men mutants.

One other interesting mystery is partial or blatant nudity. A Neph that uses his or her powers to an extreme extent tend to have an unexplained urging towards having an Out-of-clothes moment in a moment of calm almost immediately afterwards, which lasts for a few hours or even days, which would make them exhibitionists by nature, but this strange effect does not last long. Because one other consistency between any one Neph is their strong zeal for Modesty and Godly prudence and discernment. This same effect extends to subjects exposed to a substance recently discovered called Bhoonium.

The subject is not consciously aware of this effect. One interpretation is that it is the body itself that is aware of what's going on, and because of the presence of N Cells, strips away any extraneous material covering the skin. The reason for this odd phenomenon is unknown.