His eye blinked open. Slowly, he sat up. He was in a room. He didn't recognize it, but he thought he should have. He slipped off the bed and floated up to the door. Opening it revealed nothing but grey.

That wasn't right.

Was it?

"What are you doing up?"

Arms wrapped around him.

Safe

Tired

He closed his eye and snuggled into the one that was holding him.

"Let's go. Back to bed, Pine Tree."

His eye blinked open. He was a little faster sitting up this time. When he looked over the room, there was something familiar about it.

This… was home.

This… was his room.

This… was the Mystery Shack.

He got out of bed and headed for the door again. This time when he opened it, a long hallway stretched before him.

That still didn't feel right.

He made his way through the passage until he began to feel tired.

He blinked and looked around. Hadn't he been in a hallway? Everything was grey around him. Up was grey. Down was grey. Left, right, grey, grey, grey...

"No, no, Pine Tree, you need to be sleeping."

Arms wrapped around him again, but this time he looked up at the one holding him. The safe one was yellow and had one eye like him.

"Bill," he said. He wasn't sure where the name came from, but it fit.

"Sh, Pine Tree, back to bed."

He did feel tired.

The one who held him, Bill, turned and suddenly the door to his room was there, floating amongst the grey. Bill opened the door and floated inside, carrying him back to the bed and setting him in it. Bill pulled the covers over him and said, "Night, Pine Tree."

Pine Tree? Yes, that fit.

Pine Tree's eye blinked open. He sat up in bed and floated over to the door. The hallway was back when he opened it and the trip down it was much shorter than the last time. The door at the end led out into a forest clearing. That is, if forests had cloud trees and light blue floors and a sky that was a mess of greens and browns and dark blues.

Something told Pine Tree he should be disorientated by the sight.

"Ah, there you are Pine Tree."

Bill was floating in the middle of the clearing. He held his arms open and Pine Tree came over.

"Hello Bill," Pine Tree said as Bill held him again. "Do I need to go to bed again?" He didn't feel tired, but whenever Bill had appeared before, he had went to bed.

"No, not right now. Your body's almost done stabilizing. You should be able to stay up for a while."

"Okay." That made sense.

Didn't it?

Pine Tree stared out at the forest.

"Bill."

"Yes?"

"Who are you?"

"Don't worry, you'll remember soon."

Bill laughed.

Pine Tree blinked up at him.

At the demon.

Oh, that's right.

"Don't worry, Pine Tree, you're mine now. That's all in the past."

Pine Tree blinked. His memories said to stay away from Bill. Bill was dangerous.

But Bill felt safe and Bill said he was safe.

What should he believe?

What did Bill mean Pine Tree was Bill's?

Pine Tree closed his eye and leaned into Bill.

"Okay."

Pine Tree glanced up at Bill after finishing the spell he had been practicing.

"Perfect," Bill said, patting the top of the younger demon. "Your doing so well, Pine Tree. You'll be a proper demon in no time! I'm proud of you."

When push comes to shove, I'm actually proud of him.

Bill watched the pictures that flashed across Pine Tree's body. "You remember Stan now?"

"Yeah."

"Anything you want to get rid of?"

Pine Tree tilted in thought.

Bill had been helping Pine Tree as his memories from his other life came back. They usually came in waves so sometimes there were memories that were just too much or Pine Tree simply didn't care for. Bill would either destroy them or relock them depending on if he thought they were vital.

"No, not right now. We can re-check once they've settled."

"Alright, Pine Tree, then move onto the next spell."

Pine Tree would have sighed if he had a mouth. Or lungs.

Bill was working so he got stuck with bookwork until the elder demon got back. They were going over different species of monsters and while that was interesting, reading about the creatures wasn't as exciting as when Bill would actually bring them into their home for Pine Tree to study.

As he turned to the next page of the book, Pine Tree considered sneaking off to his room to practice the new fire spell he had been working on.

A monster

Screaming

Pain

Falling

Darkness

Pine Tree opened his eye and looked up at Bill just in time to see the blue flames die away. Whatever memory had overwhelmed him was gone now.

"You didn't ask," Pine Tree pointed out. Bill always asked before destroying or locking away his memories.

"You didn't need that memory," Bill said quietly.

Pine Tree looked over at the book he had been reading. It was on the chimera page. Was that what awakened the memory? He had met many monsters in his other life. Why was this one so special?

"What happened in the memory?"

Bill was silent for a moment before he pulled Pine Tree in close. "You died."

Pine Tree blinked. He had died? He supposed that made sense. He had been human in his other life. Something must have happened for him to have become a demon.

Wasn't dying supposed to be a painful experience for mortals? Bill was right; he didn't need that memory.

"Thank you."

Pine Tree shivered as fingers combed through his hair. Sensation was so… odd. Sure, he could remember it, but actually experiencing it was different. Like the difference between reading about the theory behind a spell and actually casting it.

Bill had been teaching him how to create a human form and he'd finally managed a stable one. The last time Bill had been in a human body, he had gotten momentarily distracted by the sensations - especially pain - after having lacked them for so long. Therefore, he had thought it would be good for Pine Tree to have some experience. Even more so considering he'd never technically experienced sensation.

"Bill," Pine Tree hummed, opening his eyes - more than one, and that was another odd thing about being in a human body again - to look up at his mentor. The elder demon was also in human form, sitting on Pine Tree's bed with his back against the wall and Pine Tree's head on his lap.

"Yeah?"

"I've been going through some of the memories that came earlier." He'd been spying on the Mystery Shack and the red headed girl, Wendy, had been visiting from college. The sight of her had awoken his memories of her and something had been gnawing at him.

"Is there something you want me to get rid of?"

"No - Well, yes, there's this lamb song thing, but that can be dealt with later. No, I was wondering about something else. In my memories, I was in love with Wendy, but now I don't feel anything. Is it because of my distance from my old life or - Well, can demons even feel, you know, love?"

Bill stared down at him, then laughed.

Pine Tree glared at his mentor and smacked his leg. "I'm serious!"

"Pine Tree, you didn't love Red."

"What? Yes I did! It's right there in my memories!"

"No, you only think you did because you were a naive little human that couldn't tell the difference between sexual and romantic attraction." Bill rolled his eyes and ruffled Pine Tree's hair. "You had a crush on her, that's all. Your meatsack body had just confused you into thinking you were in love with her when it really was mostly lust."

"Lust?"

"Yep, but demon's don't lust. Lust is a physical reaction based on the primal urge to mate and reproduce. Demon's have neither a need to reproduce nor do we usually have a physical form. That's why you're not as attracted to Red anymore; the lust is gone so so is most of the appeal, though the distance doesn't hurt either."

"I guess that makes sense," Pine Tree said, shutting his eyes again. "Does this mean we can fall in love?"

Bill hummed and returned to combing his fingers through Pine Trees hair. "Rarely, but yes."

"Have you ever fallen in love?"

"No."

"Oh."

Why was Pine Tree's chest suddenly so tight? He wasn't sad. Why would he be?

Bill snorted. "How can you still be so naive?"

Pine Tree glared at his laughing mentor. He sat up and pulled away. "What are you talking about?"

Bill rolled his eyes and grabbed Pine Tree by the back of his head.

Oh.

They were kissing.

This… was new. Pine Tree had never kissed anyone before. Not even in his memories.

He should probably do something.

Pine Tree brought his arms up to wrap around Bill's neck and pressed closer to the elder demon.

Bill broke the chaste kiss after a short time to chuckle against Pine Tree's lips. "I love you, Pine Tree."

The younger demon pouted in an unintentionally adorable way. "I hate you."

Bill snickered and rubbed his cheek against Pine Tree's. "Liar," he hummed.

"Takes one to know one," Pine Tree huffed, nuzzling back.

"Mine," Bill purred.

It wasn't the first time Bill had called him such, so why was Pine Tree's chest so warm?

Stupid human body.

He tightened his grip on Bill and purred back, "Mine."

They stayed intertwined, even after they had shifted back to their normal, demonic forms.

"So, this is where it happened?"

Bill had recently made a deal that had allowed for a loophole which gave both Bill and Pine Tree some time on the human plane. Because it was Pine Tree's first time there since he had become a demon, Bill had allowed the younger demon to pick their destinations. They'd already visited quite a few paranormal spots and now they were standing in the very clearing where Bill had made Pine Tree a demon.

"Yep," Bill confirmed. They were both in human form and he was pressed against Pine Tree's back, his arms wrapped around the younger demon's waist.

Pine Tree glanced around the clearing. A cliff on one side and forest surrounding the rest, it was... unextraordinary.

"I don't know what I was expecting. You already destroyed the memory of my death. Why would this place bring up any feelings?"

Bill hummed and buried his face in Pine Tree's hair. "You wouldn't have remembered this place anyways."

"Why? What happened?"

Bill frowned and pulled away to look up. Pine Tree followed his gaze to the top of the cliff.

"You had come across some information about a chimera that lived in the woods. It was supposed to be hibernating so you thought you'd come have a look, but a couple of goblins had stumbled upon it earlier that day and woke it up. It chased you. You made it pretty far, but when you got here, one of its claws caught your ankle. It didn't have enough of a grip to drag you to it, but you lost your footing and fell over the edge. You died on impact."

Pine Tree frowned. "Well, that's boring." An investigation gone wrong was okay, but after everything he remembered doing over his summer in Gravity Falls, he'd figured his death had been more interesting than that. Like sacrificing his mortal life in the process of avoiding an apocalypse or something. A hero's death.

"I felt the same," Bill chuckled, pressing a kiss to Pine Tree's cheek.

The younger demon turned to look at his love and caught sight of something on the edge of the clearing.

"That's your memorial. Red made it for you," Bill said as Pine Tree pulled out of his arms to approach the tree.

His fingers tracing the Big Dipper carving, Pine Tree asked, "How long has it been?"

"In human terms, a few months short of four years."

The fingers traveled down to the initials.

D.P. Dipper Pines. It wasn't his true name - only he and Bill knew that - but it was his name nonetheless. Just like Pine Tree, Mason Robin Pines, the Pine Demon, the Dream Star, the Dream's Mate, the Star Bear, Ursa's Dream, and Dipper Cipher.

"I added that," Bill pointed out as Pine Tree's fingers dropped to the last carving.

Pine Tree smiled and pulled his hand away. He closed his eyes and saw his human form and Bill's standing in the clearing. It was just like the ones Bill had placed in the Mystery Shack so Pine Tree could watch its occupants.

Bill frowned and glanced over his shoulder.

Pulling his vision back to his human form, Pine Tree opened his eyes and turned to his love.

"I'm being summoned," Bill growled, his blue eyes flickering red for just a second. One of his hands came up to cup Pine Tree's face and the other held Pine Tree's hand. "You can stay if you want. We can even make it a test, see if you're able to make it back to the mindscape on your own." His thumb brushed the triangle tattoo on the back of Pine Tree's hand. "And you know how to call me if you need me."

Pine Tree brought his free hand up to rest against Cipher's. "Yeah, I think I'll stay for a little bit." He leaned forward and pressed his cheek to Cipher's. "Mine."

"Mine," Cipher agreed, giving Pine Tree's hand a squeeze before disappearing.

The younger demon sighed, turning back to the tree. He frowned at the pine tree carving. Something was missing. A knife formed in his hand as he leaned forward. He began carving into the tree.

Pine Tree appeared within his room, glaring at nothing in particular.

"Hey, Pine Tree," Bill said, floating up to the doorway. "Didn't think you'd be back so soon. Figured you'd check out the Mystery Shack and Grav-"

The door slammed shut.

There was a few seconds of silence as Pine Tree floated up to his desk.

The door opened a little and Bill peaked in. Pine Tree's body was red with his arms, legs, and hat having turned white and his vest the dark red color of dried blood. "So you're mad. Do you want to talk about it? Do you want me to leave? Do you want me to kill someone?"

"No thanks, I'll do it myself," Pine Tree growled, prompting Bill to come into the room. "Where did I put that book on torture spells you got me?"

"Third shelf of your bookcase," Bill said, but before Pine Tree could float over to it, he pulled the smaller demon into his arms. "As fun as seeing you homicidal is - and it really is - you've never killed someone before or wanted to kill someone before. Hell, you've never even opened that book and it was one of the first ones I got you. I'm pretty sure we should talk about whatever happened before I let you loose on some unsuspecting mortal."

Pine Tree glared up at his love. "Since when are you the reasonable one?"

Bill groaned and let go of the smaller demon. "Gross, you're right. Fine, go kill them. Make it bloody too!"

Pine Tree snorted and his body slowly faded back to silver-blue. He leaned against Bill and said, "Some girl showed up at the clearing while I was still there."

"Red? Llama? The monster? Her friend?" Bill hummed, rubbing Pine Tree's back.

"No, on all accounts. She looked familiar, but I'm sure I've never seen her before."

"Did you get a name?"

"That's why I was angry. She - She said her name was Mabel Pines and that she was my sister."

Bill froze.

"But that's not possible. I didn't have a sister. I would have remembered her if I did, right, especially if she was standing right in front of me?"

Bill didn't say anything.

Pine Tree looked up to see Bill scowling at the wall. "Bill?"

"I shouldn't have left you alone."

"Bill, what's going on?" Pine Tree asked, pulling away.

"Nothing, don't worry about it. I'll take care of it."

Pine Tree narrowed his eye at his love. "What's going on?"

"Noth-"

"Don't lie to me. Who was that girl?"

Bill brought his hand up, but Pine Tree smacked it away.

"The truth, Bill."

Bill's eye met Pine Tree's and he almost seemed to deflate. "She's your sister."

"What?" Pine Tree asked in a quiet voice."But I don't remember..." His body was red again. "It's because of you! You stole my memories of her."

"I only locked them away."

"Why would you do that?"

"For you."

"Excuse me?"

"You would have missed her too much if you remembered her."

"I miss Stan and Wendy and Soos and you never took my memories of them away!"

"They're not Shooting Star!"

"Why does that matter?"

"She was everything to you! Everything would have reminded you of her in some way. You probably would have even remembered her before you remembered me. It took you a year and a half to be able to see into the Mystery Shack. Most of that time you didn't even remember Stan and you didn't remember Question Mark or Red until you saw them. When you miss them, you peek into the Mystery Shack and watch them. You can even check up on Red because she brought one of your pine tree hats with her to college, but Shooting Star has barely been to the shack since you died and she doesn't have any pine trees with her. You would have missed her and it would have hurt you! You would have tried something stupid like leaving and ended up destroying yourself in the process!"

"Well, I'm certainly considering leaving NOW!" Pine Tree shouted, accidently lashing out at Bill with his magic. He didn't back down though, even as the elder demon grew red. "I should have listened to my memories from the very beginning! I'm just your little puppet, aren't I? That's what you think of me, right? You think you can just jerk around my strings and I won't even care?"

"You see, you don't even remember her and look what Shooting Star's doing to you! She has this effect on you! You give up everything for her! You don't even know how many times you gave up a chance at Red - a chance at happiness just to please her! And now you're talking about leaving BECAUSE OF HER!"

"She's not the reason -" Pine Tree cut off as something occurred to him.

She was everything to you!

You would have tried something stupid like leaving…

You give up everything for her!

The red bled away from Pine Tree. "Bill… are you jealous?"

"What? Of course not! Why would I be jealous?"

"You thought I would leave if I remembered her."

"You would have! And you would have destroyed yourself!"

"Maybe, but I also wouldn't be here with you."

"Pine Tree," Bill growled in warning.

"You thought if I remembered I wouldn't be yours anymore."

"Pine Tr-"

"You thought I'd devote all my time to her."

"YOU WOULD HAVE! YOU WOULD HAVE SPENT ALL YOUR TIME TRYING TO FIND A WAY TO GET TO HER, TO BE WITH HER!"

"And I wouldn't have been with you."

Bill stayed quiet, not meeting Pine Tree's eye as his body faded back to yellow.

"That doesn't make it right, Bill. You used me. How do I even know I can trust you?"

There was silence.

Pine Tree turned away and prepared to leave.

Bill grabbed his arm.

"Bill -"

Blue flames surrounded Bill's hand and memories flooded Pine Tree. New memories, pieces to old ones, and many memories simply got clearer as a girl that hadn't been there before appeared in them.

Pine Tree realized Bill's emotions were affecting his magic because a few memories were accidently highlighted.

Dipper giving up the chance at hanging out with Wendy at the fair in order for Mabel to win her pig.

Dipper losing the chance to be assistant lifeguard with Wendy by giving the megaphone to Mabel so she could give it to Mermando.

Dipper losing time to work on the laptop because he was helping Mabel make sock puppets.

And then, in a memory Pine Tree knew wasn't his:

"Who would sacrifice everything they've worked for just for their dumb sibling?"

"Dipper would!"

"I… I'm sorry, Pine Tree," Bill mumbled letting go of Pine Tree's arm. He started to float away, but it was Pine Tree's turn to grab Bill.

"I'm still mad," Pine Tree said, pulling Bill close. "And you're going to be making up for this for a long time." He placed his hand next to Bill's bowtie. "But you're still mine and I'm still yours."

Bill threw his arms around Pine Tree and held him tight.

Pine Tree rolled his eye and nuzzled into his stupid love.

"Just so you know, if you ever try something like this again, I'm setting you on fire."

"I love it when you talk dirty, Pine Tree!"

Here's the last part for now. As I said on Shooting Star, If I get more ideas for it or if anyone wants to send in prompts or something I'll add more, but for now I'm done.

A few notes for the AU:

Dipper and Bill each have tattoos on their left arms while in human form. Dipper's is a triangle on the back of his hand and Bill's name in his cipher wrapping around Dipper's wrist. Bill's is a semi-realistic pine tree growing up his forearm. They're basically promise rings for demons and can be used to communicate with one another if need be.

The part about Dipper's "true name" was based on Bill's response in the AMA and the egyptian myth about secret names. Basically, knowing someone's true or secret name gives you power over them. Since Bill made Dipper a demon, he knows his true name.

Demons being asexual is kind of a random head canon that came to me while writing this and it just makes sense to me. I mean, I know they're supposed to inspire lust in humans - some demons more than others - but why would they actually lust themselves? What would that even accomplish? I'm sure there are some sexually active demons, but it's not because they look at someone and think, "Yes, I want to have sex with that!" It's probably more like "Sex sounds fun, that person will do!" or "I wants me some half-demon spawn!" or, you know, going back to the inspiring lust point of the conversation, they could be using sex to get stuff. Souls or life energy. Junk like that.