Prompt: Going along with the headcanon that Bill marks his older!Pines Twins, his mark allows him to follow them to their parents' home and their high school and why is everywhere else sunny?

Thick as Thieves

Bill Cipher considered the white wash walls, the hard plastic seats and the large boring, black chalkboard, and decided he didn't like this place one measly little bit.

Seriously what was this place and books? And adults. The adult to children ratio was way out of proportion, and he followed too such children down the halls of this school as they made their way to class.

See, in Hell demons didn't learn class, they were born with it.

So really, the dream demon was just an honestly confused, curious mess about most of this stuff, and judging by the reactions of his two kids, they were on opposite ends of the spectrum. But at least they seemed old hat at this day to day thing. (Except Saturdays and Sundays. Bill didn't understand any of this timeline.)

Shooting Star was no different than usual. Bubbly, bright and eager to say hi to old friends and ask about their summer and tell them about hers. (Bill winced at first, but decided it didn't matter what Mabel said because these kids were what, fifteen now? And Gravity Falls and its oddities were far enough away. Plus, everyone here seemed to know to take Mabel's words with a grain of salt.) And even though Dipper had an eye on his hat and Mabel had one on her sweater, the eye didn't let people see Bill—it let Bill see people, more specifically it let him travel with the twins, as long as he stayed near one at all times. And even then he could look through the eye in the other and see whatever it was they were seeing.

It was good to be an all-knowing omnipresent being.

So here he was, floating and looking around the school a bit absentmindedly as Mabel and Dipper stood by both of their lockers. Bill studied Pine Tree's body language. Head down, facing his small gray locker and digging through it and taking a couple breaths as if steeling himself for something. Mabel wasn't even looking at what she was doing, she was too busy talking animatedly about her many boy crushes that year with some girlfriends. Once or twice Bill saw Dipper glance over, sigh fondly, and give Mabel the correct books she needed. Mabel finished her conversation as a bell rang somewhere all around them, and everyone began filing off. A prison gang so beaten down they didn't need shackles, it seemed to Bill. He had to admire whatever it was that had broken these kids spirits, even if he wasn't sure he liked it when it came to his kids.

Cipher was a tad surprised no one believed Mabel.

He was even more surprised they made fun of the twins for it. Mostly Dipper. Stranger still, the kid seemed used to it.

When they both turned in separate directions down long, boring white halls, because Dipper had gym and Mabel had Science. Bill hesitated only a moment before slinking after Dipper. It helped Mabel had shooed the dream demon with a grin in her brother's direction, like she knew Dipper might need Bill just a little more than she did right now. Besides, Bill wasn't allowed in the Chemistry lab anyway after that whole incident with the gold liquid and the hole he put in the roof. (How he was supposed to know, Mabel said she wanted a good grade!)

Turns out, Shooting Star wasn't just a pretty face. She knew about a lot more than she let on, and her heart was always in the right place. Normally that sickened Bill, but when it came to Pine Tree, he was more than willing to trust her if it meant taking care of the kid who generally tried to tell everyone he was alright. And was usually lying.

It was only the second or third week of school, which ran from fall to spring, and already Cipher was done with this boring life and wanted back in Gravity Falls. He could sense the twins wanted that too, maybe Dipper more than Mabel. Bill didn't know entirely why, but after today gym class, he figured it out real quick.

Gym class was actual torture.

And Bill knew what he was talking about, mind you. Demon, Hell, remember? Torturing was a thing that went down regularly there. This was new but the basic idea wasn't. Make fun of the weak.

It was called dodge ball, some sick and twisted throwing game designed to filter out the strong from the weak. So far, it seemed to be working. There was a pattern, Bill picked up on it quickly. If you were thin and wiry like Dipper was, you were enemy number one in this game.

That's not to say Dipper didn't completely victimized. He did fight back, and Bill offered some help here and there. The demon knew Dipper wouldn't want him too, so he mostly hung up in the rafters and watched the game, highly amused when someone tripped or a ball popped for some strange, unknown reason.

"Oh, oh this is hilarious! Humans really know how to have fun, eh Pine Tree!"

Dipper, far below him, merely rolled his eyes and focused on not getting belted with a ball too hard. He ducked, and Bill offhandedly sent the ball ricocheting off a wall to slam into the one who threw it. Everyone laughed at the kid, and the kid and his friends glared at Dipper, who grinned sheepishly and waved.

Finally, a shrill whistle rang, like the one from this morning but closer and sharper, from an adult's lips. (What, were they dogs?) And Bill knew this meant the 'game' was over and it was time to get ready for another class.

There was a final smack to Dipper's back by a ball as the game stopped. It hit with a loud smack to the kid's spine and sent him stomach first into the ground. Even Bill winced in sympathy.

"You're gonna feel that in the morning, kid." Cipher said helpfully as he swung down to where Dipper lay face down. Dipper pulled his face from the floor and glared in his demon's general direction, but new better than to talk to thin air in a place like this.

"Hey dork, bonus round!"

"Oh, great—" Was the last thing Dipper managed before at least 4 balls smothered him briefly, smacking his arms and chin and shoulders with a much harder velocity than before.

"Hey! Game over!" Cipher snapped, swinging round to spy the kids who had done it. They were taller, bigger built than Dipper, maybe on a sports team or something. The kind of people Stan would have told Dipper to fight back too. But Stanford wasn't here right now, and this wasn't Gravity Falls.

Then the kids, shooting glances over their backs at Dipper rubbing his face on the ground wearily, actually laughed at him, mocking. Dipper's face flushed and he ducked his gaze, but the Dream Demon floating over him honed in on them and actually hissed a little bit, sort of like an aggravated tom cat. His black hands were fists.

Cipher glared, eye flashing warning red for a split second before he tugged on his magical reserves in the Dreamscape and changed.

There was a snap and a subtle shift of clothing and form in the air, so quiet you wouldn't know it unless you knew to hear it. Dipper did, and he looked up with a panicked expression as Cipher's black shoes clicked on the gym floor as he dropped his floating ability. He landed rather gracefully (only because he'd gotten used to walking a year ago) and had one fist around his cane and the other fist was just at his side, one eye narrowed in anger and concentration as he started to stalk toward the backs of the boys with a low, deadly growl.

Dipper gave a noise, half of alarm and frustration and clambered with much less grass than his demon up on his feet, and into Bill's warpath. He shoved his palms against the demon's chest and held gently, bracing himself. The last kid made it into the locker room, and they were alone.

"No, no! Bill, no." Dipper yelped.

Bill leaned like he wanted to go around, but he didn't bat Dipper effortlessly out of the way like he could have with a pinkie.

"Stop, don't do it, please." Dipper pleaded, relieved when Bill halted in his tracks at his words and turned his floating pyramid head down, one eye lifting from its narrowed glare to swivel down to search his eyes, looking for answers. Dipper realized their positions. Honestly it was like a kitten trying to stop saber-toothed tiger but it worked, Bill gave a huff of annoyance and leaned back, and Dipper took his weight off the demon's body and let Bill cross his arms.

Well, now the demon looked hurt, not so much angry he'd been cheated out of a little retribution and revenge. You haven't lived till you've seen an all knowing, ancient dream demon pouting.

"This isn't Gravity Falls, Bill." Dipper muttered, not for the first time this month, as he adjusted his shirt and patted some dirt off it after his many landing on the floor.

"You can't just go unholy retribution on somebody without it coming back to bite you. People don't lie down and believe stuff here. Especially the bad."

Bill eyed him and grumbled, turning his floating head to pointedly look in another direction. One of his boots tapped the floor. Dipper smiled in faint amusement, and it was a soft, knowing one.

"And as much as I appreciate you going to bat for me, cause you know I do," One eye peeked hopefully at him after that, perking up, "But, the last thing this old town needs is a reason to call up the church to try and exorcise something they have no idea how to handle, okay?" Dipper shuddered at the very thought of someone doing that to Bill, and the demon did soften a hair at the concern the teen showed.

Pine Tree had a point. Not that Bill would admit it out loud, but after so long he didn't really need to. Dipper saw him relax, and with a tired smile patted the demon's shoulder and headed for the changing rooms himself. Disaster diverted.

Once more an invisible, travel sized triangle, Bill wandered after his kid, all the while thinking of unique ways of getting back at those boys without Dipper being outright able to pin it on him. He'd ask Mabel later, she always knew how to get around her brother's smarts.

Dipper was right, this wasn't Gravity Falls. This was a whole new ball game.

To Bill, that just meant a challenge where he had to learn some new rules before he broke them, burned them down, and laughed at the ashes. No problem.