Branches Above, Damned Below.

Insert; Elory's flashback.

The human choked on his own blood. In seconds, Elory realized his mistake. He'd cut the boy's throat much too deep, and he was bleeding out.
"Ingrid, help me get him into the bathtub," came the distressed order.
The guardian rushed forward and caught the wavering human boy, hoisting him effortlessly over his shoulder. Elory went after, turning on the tepid water before climbing into the bathtub and craddling the boy in his lap.
"I'll have to do it now, Ingrid. If I don't, he's not going to make it."
The other guardian knelt outside the tub, face tight with worry.
"Elory, it could damage-"
"GIVE ME THE DAMNED KNIFE."
Stunned into silence by Elroy's sudden raise of voice, Ingrid mutely surrendered the bloodied kitchen knife. The boy had grown pale, nearly lifeless, cold enough that the water cooled around his body.
"Keep his head up, will you?"
Ingrid reach over, propping up the boy's skull with a flat palm. With a wince, Elory drew the knife across his wrist and forced the wound to the human's mouth.
"He's not going to take it, he's too far gone, Elory. You're going to tear him from Hell at this rate."
The guardian in the bathtub said nothing.
"Get my bag off the mantle."
"Elory, stop. He's-"
The glare his lover gave him propelled Ingrid towards the door. He returned seconds later with the black velvet satchel Elory had brought along, and set it beside the pair in the bathtub.
Elory dug through the vials and bandages, the bottles and syringes until he came to what he was looking for. Three vials of a thick, inky substance and a single syringe in which made Ingrid cringe at the size.
"Your blood. You're going to force it aren't you?", he asked, horrified at the thought.
Elory ignored him and went to work, injecting the vials, one by one, at the very site of the boy's heart. A few seconds later, he began to convulse wildly. Water soaked the floor and splashed onto Ingrid's robe and boots.
"Elory! Stop! Enough!"
Still, he was ignored. The boy choked and convulsed, a horrific cracking sound came suddenly. His spine. Elory forced his slit wrist further into the convulsing human's mouth, in which at first he gagged on the oily liquid.
"You said halfway! Stop, Elory!"
Fully horrified, Ingrid began shakily retreating backwards when Elory pulled the boy from the tub and laid him out like a doll on the water flooded linoleum. He was still alive enough that the pain hit him and he screamed, a sobbing sound that made Ingrid's stomach twist. His soul was being forced back into his body, and for that, his body was resisting. Bones and tendons snapped, joints shattered. Limp, the human boy went still.
Then he started coughing, choking, clawing at his throat as if he couldn't breathe. And Ingrid knew, it had worked. Once nearly dead organs were forced back to life, and his eyes flickered open. Pained, panicked. Inside, there was a war raging between his soul and Elory's, one human and the other not. His soul would be torn apart, and Elory's would cement the gaps death had created. His blood cells would eventually merge with Elory's. An immensely painful, time consuming process that could've left the boy useless for hours.
"Put him to bed, Ingrid. Dress him in something much larger than his human clothing and leave him in the dark."

Six hours later, The Child was born from the broken body and forced cells of a monster he swore he'd seen long before then. He was born on fire, seemingly lit from the inside. He was born in the dark, drowning in blood soaked sheets and clothing not his own. He was born, in the run down house in which his mother had once brought him first into the world and then fled shortly after.
And with that knowledge, neither of his creators were surprised when he woke with the galaxy in his eyes.