Oner Bryn was an ordinary man on an ordinary world before he was identified as a Psyker and imprisoned aboard a Black Ship for the long terrible journey to Terra.
Deemed suitable for training as an Astropath, Oner underwent years of training and extensive indoctrination before being brought before the Emperor for the Soul Binding.
The Soul Binding shaped his powers, allowing him to safely interact with the Warp and to broadcast messages through it and protecting him from the taint of the Warp
During the ritual, Oner suffered hours of agony. Touching the mind of the God-Emperor himself is also such an intense sensory experience that it completely overloads the sensory organs of all those Psykers who experience the Soul Binding; like all Astropaths who survive the Soul Binding, Oner was permanently blinded, and his personality was changed, altered; the man who walked away from the Golden Throne was very different from the man who knelt before it.
Oner served for a time in an Astropathic Choir, transmitting and receiving messages to and from across the Imperium; after a year in such service, he was selected to accompany an Explorator team delving into the secrets of a tomb world.
Blinded, but guided by a psychic "near-sense" held by Astropaths, Oner accompanied the veteran Explorators deep into the millennia-old ruins of the Tomb World; they discovered signs of some ancient catastrophe, and signs that the ancient city they traversed was only the latest sign of habitation on the world.
After crossing some invisible line, the Explorators were attacked by strange metal-bodied Xenoes armed with incredibly powerful weapons: almost half of the Explorators were killed immediately, and Oner Bryn, revealing a decisive spirit Astropaths are not known for, led the survivors to safety, utilizing his abilities to read the Warp to counter the Xenos' attacks.
After they escaped the tomb world, the Imperial Navy bombed it into rubble, wiping away any sign of the Xeno taint. But Oner Bryn determined against returning to the ordinary duties of an Astropath.
Joining the Freebonders, Oner Bryn traveled across much of the Imperium, using his powers to foretell of danger and crisis, using this information to bring himself and his Freebonding compatriots to combat them.
As Oner traveled and fought, he found his powers only burgeoned and grew with experience and use: He became so powerful that he was deemed dangerous by the Ordo Malleus; he was taken prisoner and inspected for he taint of Chaos; found free of such taint, he was recruited by Inquisitor Lurk to join the young Inquisitor's retinue and accompany him on a nigh-suicidal mission to delve into the secrets of the Tyranids.