BACKSTORY TIME!! This is gonna be a long text hehe. I’m gonna explain how Jeff became the way he did and their dynamic a bit👍
In my au, Jeff and Liu’s parents sold them to monsters in order to avoid becoming slaves themselves. Monsters value younger humans because they have more years left to live and can work longer. The average human lifespan in my au is like 30 lol.
Jeff was 5 years old and Liu was 9 when they were sold/given away. Jeff doesn’t remember his parents much, and Liu seems indifferent. They never met their parents again.
They were worked hard, already from a young age. I haven’t exactly decided what kind of labour they did yet, or where they worked. I’m torn between hard labour or somewhere more “high-society”. But anyhow, Liu learned the inner workings of their place of imprisonment and slowly but surely, worked his way up by gaining the trust of some monsters. To do this though, he had to sacrifice some fellow humans, like ratting them out when someone stole, lied or tried to flee. Liu would learn how to lie and manipulate both people and non-humans, taking advantage of every situation as much as he could. He has a plan to get out, and doesn’t care about how many people he has to step on to get there.
Eventually Liu started observing monsters occult and dark magic, also gaining access to their literature and teaching himself to read and speak the monsters language. While all this is happening with Liu, Jeff is mostly kept only working. Partly this is because of Liu, convincing Jeff to stay compliant as to not arouse suspicion to his plans. Jeff grows heavily dependent on his older brother during this hard time in his life, and this dynamic lasts throughout their lives. He’ll do whatever Liu says is best for him.
During this time, Jeff developed a friendship with another human there - Molly. She, other than Liu, was the only support and comfort Jeff had. Her presence was also a lot healthier for Jeff than Liu’s, since she focused more on hope and compassion while Liu hadn’t even bothered to teach Jeff how to read. (In the future it’s my oc Sara that has to teach Jeff how to read lol)
Until Jeff was 13 and Liu 17, they were trapped. But in secrecy, Liu had been working on a plan. The monsters had a chamber where they could turn humans into obedient and dangerous creatures through transmutation and soul-binding. Liu taught himself how to perform the ritual, and under the cover of darkness took Jeff to that place.
You see - monsters would take certain disobedient humans and through this ritual, put the humans souls into themselves (since monsters don’t have souls, there is an empty space). This in turn would transform the humans into a mindless, powerful, obedient creature than doesn’t resemble a human anymore. With the soul now being trapped inside the monsters vessel, they control everything the human does. The humans body is now indestructible, since the soul is harbored inside the monster. If you were to try and destroy the transformed human, it would be impossible and they would regenerate instantly. In order to kill one of these transmuted humans, you’d have to kill the monster with the humans soul inside.
So, how could Liu perform this ritual on Jeff since Liu himself isn’t a monster and actually has a soul? Well, by creating a completely new method - soul-combining.
Liu basically combined his and Jeff’s soul inside his own body, binding them together. This meant that after Jeff was transmuted, he could still think and act for himself. However, Liu could control him to a certain degree(Jeff does not know about this).
The transformation was incredibly painful and traumatic for Jeff, twisting his mind and body into something cold and hard, an indestructible form unfamiliar to him. It took away the warmth in his blood and the color in his skin, and Jeff could now use his blackened blood to create sharp blades that shoot out of his hands (or anywhere on his body).
After his transformation, Jeff went on a slaughtering rampage (induced by Liu manipulating his soul and body) and killed everything in his path - including all the other humans trapped there. Among these humans were his only friend, Molly. Jeff remembers killing her vividly and fully believes it’s all his fault.
In order to not have his younger brother fall apart completely after the slaughter of Molly and the other humans, Liu uses his control over Jeff’s soul/mind and manipulates him into believing he really is this dangerous, soulless, out-of-control killer that can’t feel guilt or empathy and needs Liu to control him and keep his mind in check. Jeff becomes fully co-dependent on his brother and will do anything he says. Liu doesn’t even need to use his control over Jeff’s mind.
After escaping their enslavement, they spend a few years on the run, searching for a place to settle. Jeff becomes infamous and feared in the third ring of the underworld, being known for his un-killable form and brutality. He has a few run ins with the proxies, mainly Toby. Slenderman had now been watching Jeff and his brother.
Impressed with his power and the fact that he seems to be an indestructible killing machine, Slender invites the brothers to the Manor. Liu makes a deal with Slenderman, that they get to be under the organizations protection and live in the manor if Slender can use Jeff as a weapon when needed.
Since Jeff only listens to Liu, this means that Liu gets to stay at the manor without having to adhere to the rules or do any sort of “work” for Slender, becoming necessary if Slender wants any chance of Jeff following his orders.
When they arrive at the manor Jeff is 15 and Liu is 19. Jeff becomes known quickly to the other creeps as unstable and hostile, often being referred to as “crazy” or “freak”. They do not like him and he doesn’t take well to them either, so Jeff doesn’t stay at the main house. He stays in a run down cabin a bit away from the manor, living in filth, only being called in occasionally to kill people and monsters who are causing trouble or appearing as a thereat to the organization.
This makes Jeff believe that’s all he’s good for, killing and nothing else.
My oc Sara meets Jeff when he’s 17 and she’s 16, since that’s when she arrives with her family at the manor. Then… well, that’s a whole other story.