Did Magda strike a deal with Pig, or did he wake up one day thirsting for the big milf in the sky? (Or did Magda say "Pig.. go kill for me, sweety <3" and Pig went "ON IT!!!" and started hacking people up like a professional chef for his god-wife) - vabam-fr
So Pig technically became uh, The Pig in the aftermath of an incident at his first circus- before he joined the Vaudemire Sideshow. He intervened between a parent being needlessly cruel to their offspring about a treat Pig had given them while he was entertaining (Literally just a little piece of candy, it was not worth hurting a child over, and every other kid watching Pig's show at the time got the same 'prize') and when he stopped them (by physically stepping in between them, and then shoving the adult back, when they tried to get past him again) he accidentally shoved them into a tent pole with an outstretched, steel spike that hadn't been properly sunk- killing them.
In the ensuing chaos, Pig was taken aback- he'd never hurt anyone before, in all honesty he was a young guy, literally just working with the circus to have a place to live, after he left home to seek his charge. So he stood there, relatively frozen among the chaos- and while everyone else was having a full-tilt breakdown because the clown just offed somebody, Pig found his Charge. The blade of his Cleaver is actually that very tent-spike, heated and flattened into a cutting blade and blended with other metals to enlarge the tool, because it was the blood shed by that spike that called Magda to the circus grounds.
Called "Eyeless Mag" in children's tales, she too, was a victim of circumstance. slain by her husband- a sailor- in a fit of jealousy when he believed her to be cheating on him with visitors to the tavern she worked as a barmaid in, she was split tail to snout and tossed into the ocean near Vaudemire Way's dockyard- but with a spirit far too powerful and unwilling to die with her body, she joined The Host, serving as a prophet of death and a carver of cairn stones. She haunts the area around Vaudemire Way, carving grave markers and turning tough, living soil and tangled shadowy branches to provide a place to put those who's death she's forseen. She herself is Pig's Charge, brought only into contact with him when she is needed to warn or bury the dead, Pig's mind just kinda. Broke. in the genuinely tramatic moments of discovering his charge.
He's forgotten his name, using only the clown name he performed under- face paint unwashed so long it's seemingly fused to his scales, and costume ripped and tattered now patched with pieces torn from his kills, it's not Magda's fault he is what he is- she is a charge already failed, a dead thing he is constantly calling back to the land of the living to do her duty so he can spend even a few moments in her orbit.
However, he is the only friend Mag has known, for as long as she can remember at least- and so the Cleaversworn is a double-edged sword much like the weapon he uses in her name. She knows all he wants is to protect her, and she will allow that much, as there is a constant risk of exorcists and thronebreakers in pursuit of the more docile of those who populate The Host. In turn, she has a vested fondness for Pig himself, less a goddess and more a ghostly companion, who's talent with premonition and knowledge of death has allowed her 'champion' to skirt it, time and time again.
Magda attends any death in the area of the gaplands she oversees- it's not her fault that Pig happens to be behind most of them simply to see her again.
tl;dr: Magda didn't ask for this, and neither did Pig, but if he is going to swear himself into her service, the least Magda thinks she can do is keep him from dying while he's doing it.