Jessica Sorrow the Unbeliever

John feels Jessica Sorrow's presence as she draws near:

All the hairs on the back of my neck stood up suddenly, and my heart missed a beat, as though a cold hand had closed fleetingly around it. I lurched to my feet, an almost violent shudder running through me. She was close now. I could feel her presence, feel her gaze and cold intent turned upon me as she drew nearer. I grabbed up my shoe box and clutched it to my chest like a life preserver. I moved reluctantly out into the aisle, and turned to stand facing the only door. A single great slab of solid oak, five feet tail and five inches thick, locked and bolted. It wouldn’t stop her. Nothing could. She was Jessica Sorrow the Unbeliever, and nothing in the world could stand against her. She was close now, very close. The monster, the abomination, the Unbeliever. There was a stillness to the air, like the tension that precedes the coming storm. The kind of storm that rips off roofs and drops dead birds out of the sky. Jessica Sorrow was coming to St. Jude’s, because she’d been told I was there, and I had what she was looking for. And if they and I were wrong about that, she would make us all pay. -Agents of Light and Darkness

John Taylor, as powerful as his gift is, believes that nothing in the Nightside can stand against her. Not him, not anyone.

John elaborates on Jessica's past and the nature of her powers:

I don’t carry a gun, or any other kind of weapon. I’ve never felt the need. And weapons wouldn’t do any good against Jessica Sorrow anyway. Nothing could touch her any more. Something happened to her, long ago, and she gave up her humanity to become the Unbeliever. Now she doesn’t believe in anything. And because she doesn’t believe with such utter certainty, all the world and everything in it are nothing to her. None of it can affect her in the least. She can go anywhere, and do anything, and she does. She can do terrible, distressing things, and she does, and nothing touches her. She has no conscience and no morality, no pity and no restraint. The material world is like paper to her, and she rips it apart as she walks through it. Luckily for the world, she doesn’t leave the Nightside much. And luckily for the rest of us here, there are long periods when she just sleeps or drops out of sight. But when she’s up and walking, everyone gets the hell out of her way. Because when she concentrates her unbelief on anything or anyone, they disappear. Gone forever. -Agents of Light and Darkness

In essence, she has convinced herself that nothing in the world is real except for her, and her conviction in this "unbelief" is ''so strong'' that anything she doesn't believe in disappears completely and anything that attempts to harm her (within reason as far as VS debates go, of course) fails to do so out of her simply not believing that it can.

Her "unbelief" can erase anything from people and objects to entire locations:

Her most recent rampage had been one of her worst, as she stormed through all the most sensitive parts of the Nightside, leaving a trail of chaos and destruction behind her as she searched obsessively for … something. No one seemed too sure of exactly what that might be, and absolutely no one had any intention of getting close enough to her to ask. It had to be something special, something really powerful… but this was Jessica Sorrow, who was famous for not believing anything was special or powerful. What use could the Unbeliever have for material possessions any more? There was no shortage of objects of power in the Nightside, anything from wishing rings to description theory bombs, and every damn one of them was up for sale. But Jessica Sorrow would have none of them, and people and places vanished under her angry glare as she continued her rampage. The word was, she was looking for something so real she would have to believe in it… perhaps something real enough and powerful enough finally to kill her, and put her out of everyone’s misery. - Agents of Light and Darkness

She's just as likely as not to wipe someone out of existence the moment she meets them:

Anyway, I found what Jessica Sorrow was looking for, and now it lay in the shoe box I was crushing to my chest. She knew it was here, and she was coming to get it. My job was to present it to her in exactly the right way, so that it would defuse her anger and send her back to wherever she went when she wasn’t scaring the crap out of the rest of us. Assuming, of course, that I had found the right thing. And that she didn’t just storm right in and unbelieve me out of existence. -Agents of Light and Darkness

Destroying a 500 lb door is something she can do quite casually:

The heavy oaken door was reinforced with heavy bands of black iron. It must have weighed five hundred pounds, easy. It didn’t even slow Jessica down. Her thunderous feet marched right up to the door, then her fingers plunged through the thick wood and tore it like cloth. The whole door came apart in her hands, and she walked through it like a hanging curtain. -Agents of Light and Darkness

So much as looking at the container of the item John had for her was enough for it to disintegrate:

“Hello, Jessica. You’re looking… very yourself. I have what you need.”

“How can you know what I need?” she said, in a voice that was frightening because it was so nearly normal. “How can you, when I don’t know myself?”

“Because I’m John Taylor, and I find things. I found what you need. But you have to believe in me, or you’ll never get what I have for you. If I just disappear, you’ll never know…”

“Show me,” she said, and I knew I’d pushed it as far as I could. I reached carefully down into the pew, picked up the shoe box, and presented it to her. She snatched it from me, and the cardboard box disintegrated under her gaze, revealing the contents. A battered old teddy bear with one glass eye missing. Jessica Sorrow held the bear in her dead white hands, looking and looking at it with her wild unblinking eyes, and then, finally, she held it to her shrunken chest and cuddled it to her, like a sleeping child. And I began to breathe once more. -Agents of Light and Darkness

The only reason John isn't deader than MySpace right now is because she believed in him and what he had for her long enough to actually find out what it was. (It was an old teddy bear she used to own.)

She smiled down at the battered old bear in her stick-thin arms. “I’ve enjoyed our little chat, John Taylor. Made possible by this place, and this moment. Don’t ever try this again. I wouldn’t know you. Wouldn’t remember you. Wouldn’t be safe.”

“Remember the bear,” I said. “Just maybe, it can lead you home.”

But she was already gone, striding out of the church and back into the night. I let out my breath slowly and sat down on the front pew before I fell down. Jessica Sorrow was too damned spooky, even for the Nightside. It’s not easy having a conversation with someone you know thinks she’s only listening to voices in her head. And who can drop you out of existence on the merest whim. -Agents of Light and Darkness

Her sheer willpower is the only thing holding herself together. Were it not for that, she would disappear from existence on the grounds that she no longer believes in herself.

“I don’t know, any more. That was the point. My past was so appalling, I had to make myself forget it, had to make it unreal, had to make it never have happened. But in doing that I lost my faith in reality, or it lost faith in me, and now I only exist through a constant effort of will. If I ever stop concentrating, I’ll be the one to disappear. I’ve been alone for so long, surrounded by shadows and whispers that mean nothing, nothing at all. Sometimes I pretend, just to have someone to talk to, but I know it’s not real… But now I have my bear. A comfort, and a reminder. Of who and what I was.” -Agents of Light and Darkness