The Lost Sinner is a prisoner of Sinner’s Rise. Her imprisonment is self-imposed, as the exit to her cell is wide open. She eternally punishes herself for the sins of her past. She does this by remaining imprisoned, and by wearing her penal set. A mask that pushes spikes into her face, a straight-jacket with a belt that tightly cinches, or binds her waist, handcuffs that restrict the movement of her hands, and a skirt that the guilty wear in shame.
The Lost Sinner committed what some would believe to be the ultimate sin; attempting to light the First Flame. Any context for her crime is not included, but the events described happened a long, long time ago as it is repeatedly mentioned in her item descriptions that “by now, no one knows who this was used to punish, or for what reason”. We can draw a number of inferences about the Lost Sinner. It is evident that she hates light, as she will extinguish the braziers on either side of her when the boss fight begins. But interestingly, she was willing to leave them burning prior to the Chaos Bug entering her mask. This indicates that she is controlled by the small Chaos Bug we see in her opening cut scene. We know that the Witch of Izalith was transfigured into such a bug, and became the Bed of Chaos, mother of demons. We also know that these creatures have the ability to control others or at least influence their actions, because of the unfortunate fate of ‘bad-ending’ Solaire. It seems likely then that the Lost Sinner is controlled by the Chaos Bug. It may be that the “she” the item descriptions refer to is the Chaos Bug, as the Lost Sinner herself seems to be very masculine. Perhaps, the Lost Sinner battles with the Chaos Bug for control, and that is the reason for her self-imposed imprisonment, as she fears that if she were free she may be driven to try to commit the same crime.
Certain things relating to the Lost Sinner indicate she may be insane. The floor of her cell is completely covered in writing; strange symbols that are unreadable to us. She is wearing a straightjacket, a common restraint amongst the mentally disturbed. Her cell contains many chains, all pulled to a central point on the floor, indicating she was once bound with them, but escaped, and could have escaped the cell altogether.
The Lost Sinner possesses the Soul of a Great One; she holds the remnants of the Soul of the Old Witch of Izalith. Eons have passed since the Old Witch of Izalith walked the land, but such was her power that it persists even now.
The history of the Lost Bastille indicates that there was once a Lord who, attempting to quell the rapid spread of the Curse across the land, imprisoned those branded within the Bastille, which was turned into a prison. A tower was built to contain even more of the Undead, but in the end it did no good. The tower became known as Sinner’s Rise. Those imprisoned were left abandoned to rot. The events described appear to have taken place when the Kingdom of Olaphis was around. We hear from Straid a very similar story, and know that Straid was betrayed by the people of Olaphis who feared his sorcery. In this climate and culture the cure for the Curse must have been desperately sought, as it is now. It seems likely that the Lost Sinner was one born into the time of Olaphis, though this is by no means a certainty as in every age the Curse has come again and people have been driven to desperation.
The presence of two pyromancer phantoms in the New Game plus boss fight against the Lost Sinner indicate that she had a following. Why else would these two phantoms from adjacent cells come to her aid? These pyromancers are known as Prisoned Sinners. Another character we meet in the Lost Bastille known as a sinner is Vorgel the Sinner. This phantom wears the armor of Drangleic soldiers and seems to have carried the Bastille Key or protects it. This Bastille Key allows access to the Sinner’s Rise doors and an easier victory over the Lost Sinner, prompting the question; are the two connected? While she may have had people who supported her, the fact that the properties of her greatsword are unknown even to her may indicate that it was given to her as a punishment. We know that it becomes weaker the more sinful the wielder, and perhaps this fact eternally reminded the Lost Sinner of her plight.
We must also ask, what is so bad about trying to light the First Flame? Shalquoir says the Lost Sinner tried to light the first flame (not re-light it), indicating it had been extinguished. We can already see a similar situation to that of Gwyn and the Witch of Izalith. The Witch of Izalith attempted to duplicate the First Flame from a soul, but instead created the Flame of Chaos, a twisted bed of life. Perhaps it was knowledge of this history that caused the Lost Sinner to become so vilified by others and filled with self-loathing. Whatever her crime, it would seem the Lost Sinner has paid dearly for it, and we cannot help but pity her (even as she tries to poke our eyes out).