William Solis's Master Post
William Solis, AKA Billy, Will, Sol, or Solis, is a completely revamped version of Bill Cipher. This revamp is called The Shape Eater Factor, or TSEF.
He was born into an aristocratic family of squares and circles. Despite him being an equilateral triangle, they made sure he got the best of care and treated him kindly, while everyone else save for Kryptos and Hectorgon (Karlos Naica and Hector von Gahn here) treated him extremely poorly. But one day, his dimension was flooded with shape eaters, and became apocalyptic. His family was the last to go, and he got his x-shaped scar and jacket torn trying to protect them. With a burst of power and strength he never had before, he eradicated every shape eater with one fell swoop, leaving him the last one left (?) in his realm. He has nightmares about this, to this day. All he had left of the realm were a tablet and the clothes on his back. Alone, he traverses other dimensions, helping people, and has low hopes that his people will be reborn.
His realm still stands, razed and grayed out completely, and he uses it as a sorta home base for whenever he's not traveling dimensions, living in the forest so he won't have to look at the utterly destroyed buildings.
Appearance
by me
by @sunnihope
Some Facts:
William's voice claim is canon Bill, but just imagine that it's softer, more gentle and sometimes stammering.
he's a sweetheart. A bit jittery and paranoid thanks to bullies and the incident that destroyed his livelihood, but a sweetie nonetheless, as he is a friend to all living things.
absolutely loves sweets, especially hot chocolate.
he has an especial soft spot for children
he doesn't like being unexpectedly touched, nor does he like his tail and horns being touched. (He gives children a slight exception.)
his tail behaves like an animal's, in that it wags when he's excited and curls inward when he's upset, among other things. It's even prehensile!
appreciates expected hugs and cuddles
sometimes the scar hurts, and he doesn’t know why.
when possessing someone, which isn’t often, their eyes turn a brilliant, haunting blue, like his eye.
he doesn’t like his occasional supernatural hunger (souls, flesh, blood). He’s taken to bringing pork around with him to sate it.
his eye becomes a full-on slit if he’s hungry or angry enough, the latter of which is extremely rare.
his extremely kind nature led him to develop powerful healing abilities, to the point that he can cure terminal and otherwise incurable diseases.
he has a stammer. He almost always did, but it got worse a while after the Shape Eater incident.
William doesn’t really sleep, and if he does drift off he can't sleep well because of nightmares, so his dark circle formed as a result of that.
unlike canon, he wasn’t trapped in a dream or nightmare realm, so he can physically exist in any dimension he hops into.
William despite being a triangle is also very intelligent, very observant, and has an excellent way with words, especially if his anxiety doesn't get in the way.
he was studying to be a governor before the dimension was flooded with Shape Eaters. He really wanted to change things.
his birthday doesn’t exist in his and other dimensional calendars. The Shape Eaters and the burst of power left little behind.
he actually isn’t the only survivor... he just thinks he is...
Family
William's family were very aristocratic, rivaling the higher ups. They were also very kind and happy people. But they and the higher ups (the powers that be), were often at odds because they wanted a change and the powers that be knew no other way for their society to be.
He is the third child out of seven, and all of them were fond of William because of how they were raised. Billy was often in charge of taking care of the younger and youngest with his older siblings' help when his parents went to work, since his parents thought he could learn a thing or two about caring for children.
Euclydian Society
Triangles are the lowest, only set to become infantry, slaves or homeless. They usually don't speak grammar properly, and are taken out of school or drop out before high school.
Squares and circles, William's family makeup, are higher up, despite squares having just one side more than a triangle. They get to be lawyers or priests in particular, but they're not exactly limited to these. In this dimension, it's also possible for squares and circles to birth a triangle, but not the other way around.
Stars are rare, and rectangles and pentagons are the same as circles, squares and rectangles. Other shapes also exist, of course.
Wiliam's family sought to change the society, almost always butting heads with the powers that be, who were often diamonds, but the powers that be knew no other way.
There are three planets. One for slaves and infantry, since no one wants to be associated with them. Only reason shapes go there is to hire a veteran or get a slave to do their bidding. Another belongs to the governors, the powers that be, because they're higher than everyone else. The last one is just shapes living together and doing their daily jobs and lessons and so on.
On each planet are warps, similar to the Warp Pads in Steven Universe, but slaves and infantry can't use them unless they're with someone who can. There's a magical signature embedded within every shape's frame, dictated by their family bloodlines, that either allows or disallows use. William still has the Solis signature even with his transformation into a demon, but for extra proof his family gifted him a tablet that also contains identification, since they knew the guards of each warp won't take kindly to a triangle having access.
The insignia on the back of his tablet is this:
It also pops up in energy readings in general. Every family has an insignia, and it's different for every single one.
Shape Eaters
The Shape Eaters are vile, mindless creatures like the Heartless, only caring about eating shapes and destruction. A realm that has even one in it is doomed. They aren’t really supposed to exist. But they do. Only those affected by the Shape Eater Factor can truly kill them, and they become light gray ashes when they die.
If a Shape Eater contacts a shape without killing them, the shape gets these powerful abilities akin to a demon, based on their interests, and thus transform into a demon; they also get the ability to dimension-hop and basic abilities such as shields and deflection, possession, shapeshifting, etc.
Involvement in Gravity Falls
William Solis met Ford around the time canon Bill met with Ford, only not in a dream. The demon met Ford when the man was sleeping against a tree. He sensed that the guy was troubled with other issues since he looked peaceful in sleep, and waited beside him for him to wake up. Ford at first thought he was dreaming when he woke up, but Billy assured him that wasn’t the case. They talked, and Billy offered to help with anything Ford needed. And he did genuinely help—patching Stan’s and Ford’s relationship back up, helping Fiddleford and Stanford with their studies on weirdness, helping Fiddleford cope with the weirdness around, and eventually, after Ford expressed interest in seeing other dimensions, helped create a true Interdimensional Portal*, marking Ford and everyone involved a star in Oddology. The Pines and McGucket families flourished with this. Eventually, Ford began to think of Billy more as a fellow Pines than a Muse because of how close they became and all the issues Billy single-handedly fixed, and offered that he could come visit Gravity Falls at any time.
As a result, the memory gun and the Blind Eye don’t exist, and the people of Gravity Falls are much more competent.
* The possibility of parallel selves touching causing the dimension to fizzle out doesn't exist here. If what PF said about it was even true.
Writings / Stories
AO3 Series