Unreal Potential: Mercure
Byron's body is currently inhabited and given life by the Blade of Lesser Son lodged in his back. What exactly this entails has lacked an explanation until now.
The Blade of Lesser Son was the Ryeas of an entity that gave its existence for its sibling. In order to perform such a selfless act, the Lesser Son had to separate all of their negative intent from their form... of which they held much. Using the blade, they had cut away at themselves, piece by piece, until only their good heart was left.
The silver substance that oozes from the blade into Byron is the manifestation of that evil, endlessly empowering and corrupting whatever it touches. Atop rendering Byron all but impervious to damage, the Blade itself allows Byron to tap into that most heinous, vile power of the Unreal: 'Mercure'.
Mercure is a frenzied state like no other. If a mortal being without a Ryeas is struck, but not killed, by The Blade of Lesser Son, Byron can chant a lost piece of the Santima Avenna to trigger Mercure. Within a day, the mortal will lose all sense of self-worth. Within the week, they will become paranoid, afraid, and aggressive towards those who near them. Finally, and most despicable, the victim will give in to their darkest desires... they will enter a place so deep in vile intent, their minds will shatter to avoid the pain of guilt. The crimes enacted during this state will be left undescribed, as they are too loathsome to name in good company.
All those possessing a Ryeas, mortal or otherwise, can still be subjected to Mercure if one of two conditions are met:
First, the subject may be weakened to a 'Silent' Rapture Rating. This is not expected.
Second, and slightly more likely, the intended victim must be willing to sacrifice themselves for another.
The condition can be cured by the absolution of one's sin- to act in selflessness even while the early stages of Mercure are taking place. This cannot be done if the victim has believed knowledge of the cure- the act will be disingenuous, no matter the desperation of those who wish to save the victim.