Radiance is a part of the Soul Aspect of the Divine Fysa.
This is an active fysa. This fysa allows one to manifest their soul as a physical weapon. The weapon is unique to the user, and can either be symbolic (a sphere, a disk, rays of light, etc) or literal (a glowing sword, staff, spear, etc). The weapon cannot be lost-- it can be un-manifested and re-manifested at will, and strong users can even summon up to 3 copies of it.
Radiance does not cut or bludgeon like a normal weapon-- it creates a burning sensation, and drains the fysa energy of those it attacks. This is important, as they spend energy to be summoned, so if the user fails to land any hits, they'll be draining their own energy.
Like halos, radiance can vary in shape, brightness, or color reflecting the individual's soul and emotion.