Neutronials are seldom seen, even among the Cosmic entities, as their creation requires a complex set of circumstances that is only rarely met. Originally, all Neutronials were Astrals, but, having left the heavens by misfortune or duty, they lost faith in their purpose and the nature of humanity after seeing the horror human nature is capable of. Through an old eldritch quirk in the nature of Astrals and their role in the Constellations, this lack of faith renders them immune to all magic.
Astrals are beings of emotion, more so than most creatures, and as a result they are profoundly affected by the world around them. The glow and power of an Astral stems from the faith they have in magic and their duty to protect it. When, for whatever reason, an Astral loses faith, they become a Neutronial. The transition is rapid and physically manifests only as the loss of the Astral's glow, echoed by the death of the star that Astral was associated with.
Astrals are not particularly powerful, beyond their ability to generate great quantities of light. Neutronials, however, are treated with fear and mistrust by the Secrets, not because they themselves are a threat but rather because the Secrets have no way of controlling them. This is because the only ability of Neutronials appears to be complete immunity to all forms of Magic, though they are still limited by the physical limitations and requirements of being alive. More worrying still, this immunity extends to anything touching the Neutronial's bare skin.
Many Neutronials side with the Others out of bitterness and anger, and are rapidly elevated to high echelons of Abyssal authority due to the usefulness their immunity offers.