"Surprise, Bill."

Bill's eye widened. How?
How had this stupid, ordinary human been able to hide this from him just by focusing on other thoughts? And since when had he been able to control his thoughts so well?!

What have you DONE?

Dipper did not answer.
Something was happening to the young man, he was still awake, but he was lying on the floor with a seemingly terrible headache, making pained noises every now and then. Bill didn't understand, and it made him furious. Dippers mind seemed to alter itself in some way, some kind of force within it changed. Things only a dream demon would notice.

What was that gun? Are you trying to erase me again? You FOOL!

Dipper seemed to laugh. Bill couldn't see it, still in his mind, and he decided to leave right now. There was nothing he could do to prevent Pine Tree from destroying himself, but he was done taking any part in it.

And that was when he realized.
He couldn't leave.
There was no way out of this mind, not anymore.

YOU WILL TELL ME WHAT YOU'VE DONE, RIGHT NOW!

Bill's eye went red, his body black, he changed his form to his usual triangular shape and then to a gigantic six-armed pyramid within Dippers mind. He tried to use his every bit of energy to break out of here. But nothing worked. Some kind of force field, opposing to his own energy, was keeping him in. The demons body started to shake out of anger, and something else he couldn't quite recognize.

THAT'S IT.

Bill used his privilege of being inside Dippers mind to make the young man fall asleep, dragging him into the mindscape. Literally. He had grabbed Dipper by his hair, dragging him over the grey floor, then smashing him against the wall of his apartment, again, and again, and one more time. Making him bleed. Getting even more furious remembering that the human enjoyed this.

"You think you can outsmart me, Pine Tree? Do you know who you're dealing with? DO YOU KNOW WHAT YOU'RE DEALING WITH?", the demon screamed at him, throwing the other to the floor and stepping on him, hard. His one eye stared down at Dipper, and every other human being would have been intimidated, scared to death, begging for their life.

But Dipper Pines laughed.

"You tell me, Bill."

Suddenly, Bill was forced back into the human form he had picked out of Dippers dreams, and the demon fell to his knees. He was too confused to even struggle. He did not understand what was happening, at all. It was almost as if he had… lost control. Completely. Bill's eye was wide and he now knew what the strange new feeling might be.
Could this be what humans called… fear?

"What have you done?" the demon asked one more time. He still couldn't believe any of this. He couldn't believe that any human would be capable of doing something like this.

Dipper smiled weakly. It was almost a sad smile, pitiful even.
"You said you didn't like how you weren't in control anymore, didn't you, Bill? Well, here's the thing: You never were. You underestimated me greatly. Did you really think that after all these years I have spent obsessing over you, I wouldn't be well prepared for your return? Did you think that after I've beaten you within the mindscape when I was only 12 years old, I wouldn't be able to perfectly control my thoughts 8 years later?"

No. That couldn't be. No one had ever been able to do something like that, no one…

"The gun is similar to the memory gun that erased you back then, but not quite the same. Great uncle Ford and me build this one together after Grunkle Stan had recovered his memories. It surprised me that you thought I was able to convince Ford just like that. You, of all beings out there, should know his paranoia very well. He wouldn't shut up about you coming back until we created this."

A picture of the gun Dipper had shot himself in the head with earlier appeared right behind him.

"We came to the conclusion that erasing you out of someone's head wasn't save enough. So this gun was made to trap you inside a person's mind instead."

Bill stared at the young man in disbelief. He was still on his knees and unable to move. Unable to change his form. Unable to do anything at all. Dippers mind control was stronger than his own, something no human had ever been able to do. And Bill came to the horrible realization that everything he had just been told was true. He had not been in control from the start. Dipper had always just manipulated him into doing whatever he wanted, and now he was able to force him.

This couldn't be true, right?
He was an all-powerful demon, a being of pure energy with no weaknesses, right?
But this was the mind of Dipper Pines. And he couldn't leave.
He had made a grave mistake.
He should have left when he still had the chance.
He should not have agreed to the deal.

No, no, no, NO!

"Y'know", Dipper sighed, slowly walking around the demon in circles, "I was hoping that I wouldn't have to do this. Because I really prefer you being the dangerous, sadistic and bloodthirsty demon. The one who forces me into submission. I would've never expected you to become so soft. What was that about, Bill? Did you actually want to help me, by signalling Mabel and then leaving me?"
He laughed a little.
"The gun wasn't meant to be used for this, but who cares. It's too late now."

"You're really not much of a human anymore, kid."

He didn't know what else to say. This was utterly wrong. Not only had the kid completely turned around the situation between them, he also correctly interpreted Bill's every move. When had his actions become so easy to read? When had HE, the demon of nightmares and master of manipulation, become the victim of manipulation?

Dipper was now right in front of him. There was an almost gentle smile on his face. He brought both his hands to Bill's cheeks, and kissed him. The demon wished nothing more than to be able to change out of this form, but Dippers pure mind-force didn't allow him to even lift a single finger.
"You started to care about me, didn't you?" Dipper asked, "That's sweet. No, really. I'm kind of glad you do. I don't know if what I'm feeling about you is love, or just a messed up obsession. But what's the difference, really?

Bill's look was deadly.
"Don't talk to me like that. I don't really give a shit about you, Dipper."

"Oh? No affectionate calling me 'Pine Tree' or 'Sapling' anymore? You're hurting my feelings."

"I will find some way out of this. And I will make you regret this. I will find a way to kill you, Dipper Pines, and it won't be the last thing I do. I'll torture your soul even after your death. You really shouldn't mess with things you don't fully understand."

"I don't even understand myself, so I really don't care, Bill."
Dipper knelt down in front of him. He started to kiss the demons neck and softly let his hands wander over the others chest. Bill inhaled sharply. This was really not how things were supposed to be.
"Never thought I'd see you like this," Dipper said, his hands moving to Bill's crotch and starting to rub him through his pants, "I like it. Not what I prefer, but enjoyable anyways." The young mans voice was so cold, so empty of every emotion, and yet there was a certain weird sadness to it. Bill closed his one eye. This wasn't happening, right?
This couldn't be happening!

Suddenly, he felt himself move. He didn't move on his own, it was the other controlling him. Like a puppet. Oh, the irony. Bill lied down on his back, lifting his hips and slowly taking off his pants, all while Dipper placed kisses all over his chest.
Bill's body started to shake a little, but that was actually him struggling at full force against what was happening. It was pathetic that even when he tried to fight back with everything he got, he couldn't even put a scratch on the absolute control Dipper had over his own mind.
Dipper rolled his hips against Bill's, a moan on his lips. He pulled the demon into another kiss and Bill couldn't help but start feeling aroused, too. Fuck. He didn't want this, because he was a demon, and demons never succumbed to the wants of others. But he had become somewhat addicted to his touch, addicted even to this pathetic human form Dipper had dreamed up for him, addicted to the way the young man moaned and screamed his name when he fucked him senseless.
"Stop", Bill breathed out, hating himself for how fucking weak he sounded.
Dipper smiled a little, softly kissing his cheek. Bill hated it.
"I won't stop controlling you unless you're willing to dominate me like you always do. If you don't want that, I'll make you. You have nowhere to go anyways."
Bill couldn't even decide what was worse. Being completely under control while doing this was horrible, but he honestly didn't want to take action right now, either. He felt utterly defeated.
"Do whatever you want" Bill said, and closed his eye.

He had lost.

[Authors Note: Hey to the few people reading this, I'm not sure if I will continue the story here, but you will find it - and me - under the same name on Ao3.]