Finally posting this in celebration of the chaos that is Halloween and these shows.

This is an expansion of a crossover sentence I did in my Gravity Falls sentence story collection Boscaresque. The basic idea is that I take one word prompts and write 20 Gravity Falls fanfictions each week, but each is only one sentence long. This Soul Eater crossover came into my mind, and it's third one that's had a extension request, this time by AwesomeOliver, so here goes! Thank you so much for prompting so many sentences and this entire story!

Just going to say that the thoughts behind this story are really disjointed as I write, mainly because I've been using it as a warm up to getting into multichapter works. Which is probably why it took so long, but I'm happy to say I at least got it done!

Finally, this is clearly an AU, so I'm taking some liberties with canon of both series, even though a lot of the Soul Eater ones are sticking my finger in plot holes that always bugged me.

The original story (sentence):

Ancestor

Cipher watched from the shadows under the stain-glassed window as the twins switched from meister to weapon in fighting the latest monster hiding in Gravity Falls: this little training ground away from Death's watch was the perfect place to train the latest Pines family weapons, and the old pair of witches hiding on the outskirts wouldn't know what was coming once the twins consumed their 99 monster souls; wouldn't the Kishen be proud of this little demon once he unleashed the chaos of two stolen Death Scythes on Shibusen.

For an all-knowing god, Shinigami could sure be blind.

Bill Cipher at least had never claimed to know everything, only lots of things. He knew the answer to any numbers of codes and riddles. He knew the true secret of Excalibur's wielder. He knew that no matter what spells or tricks witches tried to play, they would never be able to outmatch death.

But he also had knowledge that was more useful for his ultimate goal. It wasn't easy to define "create as much chaos as possible and have fun while doing it" as a master plan, but he was a demon, after all, and that's what came from being a creature of madness. If anything, Bill quite enjoyed the madness, it was what allowed him to retain his sense of humor, surprise those he "favored" with his off the wall gifts, use that punny human first name as a moniker rather than the more intimidating Cipher witches liked to refer to him as.

It's also what kept him interested enough in watching all of humanity, not just the special snowflakes who would have an impact on the future game. He wasn't called the All-Seeing Eye for nothing, and Bill Cipher never forgot a face.

Maybe that's what gave him an advantage over Death. After all, he tended to go most people's entire lives without seeing them, only to come in and try to exert his full power in their final moments. It bred resentment among humans, which was amusing given their love of the order he so voraciously, if oddly, protected.

Also due to their love of keeping those delicious souls in their bodies.

But Cipher had a sneakier way of going after souls. He wasn't about to reveal himself as a Kishin on Death's radar: even if he could fight off whatever young weapons and meisters Shinigami threw his way, that'd only pique the interest of the Death Scythes. And Cipher wanted to be stronger before he got involved with them, preferably behind the shadow of someone stronger with a more vested interest in killing Shinigami, like Asura.

Bill had to admit he didn't mind the old geyser. Shinigami tried to kill him on principle, yes, but he also had that little twitch of insanity that revealed that the madness had gotten to him too, and he passed it on to all the little weapons and meisters as surely as he did his hatred for demon-kind. But just because they had a predator-prey relationship didn't mean they had to have a hate-hate one. Bill tried to kill humans on principle, suck their souls right out, but the smart ones still went and built the pyramids for him.

Souls were just funny that way.

But that funny attitude tasted delicious, even in the little sips Bill took to survive. Eating people's dreams rather than their souls wasn't as filling to the demon (who called himself a dream demon as another way to cement his change in diet as a disguise), but it left living humans rather than a horde of monsters and zombies Shibusen needed to put down, and that allowed him to mark his territory or migrate at will. It may have the fun side effect of spreading madness while stealing all semblances of intelligence and sanity away (it is sucking off pieces of the soul bit by bit after all) but that only made the residents of Gravity Falls all the more amusing.

The small town also had the benefit of having very special residents in the Pines family.

Now of all the things that made Death a fool, his blindness in how he sympathized with humans immediately before and after having a human-like son set the stage for his own demise. Bill knew how to act like people: you talk to them, become their friend, and backstab them before twisting their words into a binding contract to make them your helpless puppet! (He had seen it enough in all of the major governments from his vantage point on the back of every dollar bill to know that that's really how the human world works.)

But Shinigami got it through his dumb little head to believe that humanity was defined by free will, by independent choices and thought as if that was the cornerstone of order rather than a symptom of chaos. He gave a choice to all of his weapons and meisters to leave Shibusen and their responsibilities at any time, no strings attached, if they wanted to go about normal lives.

And they did for all kinds of stupid reasons! Love, normality, greed, opportunity to use their skills in the private sector. One meister who had gone so far as to train a death scythe left her kid behind and ran just because of a breakup! It made the image of Bill hidden behind Death's throne and the others all throughout Shibusen become less of a spy feed and more of reality show live-streaming comedy and entertainment. There was always some weird mix of action, bad drama, disgusting romance, and horridly bland jokes going around for him to snicker at while focusing on more important things, like beavers with chainsaws.

He had heard someone describe that odd mix of genres as something called a "Shonen" but he found that decidedly un-American for an patriotic icon such as himself to be using.

But Death's free pass for retiring weapons, combined with his complete and utter focus on his precious school and his son in the past few decades, led to things slipping through the crack between the god's two eyes (another reason why one was better. It also doesn't distract you with useless things like depth perception. And triangulation- heh, it's funny because he's a triangle.) And Bill was more than willing to take advantage of that.

So when twin weapons had stormed out of Shibusen, unable to find a meister able to wield both a gun and bronze knuckles simultaneously and refusing to be split up, Bill of course made sure to keep a special eye on them. And when Stanford and Stanley Pines disagreed about their childhood dreams to sail around the world the demon was more to take advantage to help guide Sixer on his route to discovering the secrets of Gravity Falls, and after a few years of friendship (and hand-picked dream-eating on Bill's part) Ford stopped associating Bill's tips towards eating the souls of defeated monsters with bullies and Shibusen and eventually started following through.

It stopped what had been quite the free feast for the dream demon, but hey, the new Society of the Blindeye thing Fiddleford invented when he finally lost it far expanded how much of the residents' souls Bill could get away with.

Ford had reached 83 of the necessary 100 souls when he found out about some of the demon's other aspirations to pass the time, and next thing the demon knew Ford was gone, the portal was shut down, and he was left with the Stan Pines who dreamed of adventure but sensed the inherent danger in the supernatural and was smart enough to want nothing to do with it.

Well, nothing to do with it besides keeping in handy a few close contacts at Shibusen who Bill would not appreciate having tipped off about his existence should an attempt to mold Stan into his perfect weapon went wrong. Just needing to peep on Spirit Albarn the few times he went drinking with Stanley made Bill sick.

But when yet another set of twins showed up, another set of twin weapons, Bill knew he was back in business.

Yes, it would be hard tricking two kids into killing over a hundred monsters each, yes it would be even trickier to teach them about weapon forms behind the scenes, and Bill even groaned the first time he faced the dilemma of how is Asura's name was he going to convince these two twelve year olds to start eating these monsters' souls? before Shooting Star stared at the object, commented that it was so shiny and slurped it right up - he knew he had a reason to favor the chaotic self-proclaimed goddess of destruction. But Stan Pines was oblivious to this set of twins' inhuman states, the kids were eager to try out their 'magic shapeshifting powers' after he was sure to turn Pine Tree into a pen knife and Shooting Star into a grappling hook while fighting over their Grunkle's mind, and given how many adventures they were having (and how little supervision Stan gave the kids) it was all too easy to guide the children into the woods in search of adventure.

And setting just enough of his monsters after them to slowly edge up the soul count while keeping them both alive and ignorant was even more of joke when he spied on Shinigami's pupils fighting over every mission.

Bill was sure he would make a better teacher for these weapons that Death would. And hopefully by the time Stanley Pines got that portal up and Stanford back the kids would already be in too deep for their great uncle to save them from becoming Death Scythes, and all of the not-so-positive attention it would bring from Shibusen. If all went according to plan, Ford would find himself forced to stand by Bill's side or face losing his family to the one group of people he was even more wrongly convinced didn't care than his brother. Add in a sure to be unstable portal, the potential for a dimensional rift, and the utter heartbreak that was sure to come and Bill knew it'd be quite the party.

It wasn't like they necessarily needed to defeat Death or anything, just the fight would stir plenty of Madness and that all went Bill's way. Even if they lost, it wasn't like the twins had any suspicion that Bill happened to make a deal with the pair of witches living on the edge of town that he'd offer them protection from Shinigami in exchange for a future favor and their continued residence.

Yet there was something in the back of the dream demon's mind that led him to believe that maybe, just maybe, the Pines could win. It was their home turf (which given the terrain and secrets hidden under Gravity Falls actually meant something), the power of what would hopefully be nearing three Death Scythes, and Bill's favor in making sure that however the fight broke out, it'd be clear that Shinigami started it.

The demon couldn't wait to see the look on Shinigami's face when he realized that death scythes could technically be forged without him. By a Kishin, no less. And perhaps this little stain on Shibusen's sickeningly illustrious record would cast doubt on a few more weapons' minds.

But more than anything, these kids were a force to be reckoned with because they were together. Bill glowed as he watched Pine Tree and Shooting Star dance from form to form, Pine Tree always keeping an eye on his sister's back when his twin got distracted and Shooting Star preemptively catching her brother when he stumbled. Not even Shinigami had seen a weapon-meister pair more in tune with each other's souls (Bill knew because he had seen all Death had and more), and the twins' dual-weapon state made that double.

Their weapon forms may not be the most intimidating, the demon thought while Shooting Star slashed her brother's knife from into the hide of a Gremoblin, only to change into her grappling hook and shove them both back before the monster could counter-strike, but the strength of the kids' souls were all that really mattered in a serious fight. They truly encapsulated the human phrase looks could be pretty deceiving.

The triangle floating over the top of Shibusen would all too happily agree.