So, actually, I had planned to write a fun AU with is 90% bad jokes and 10% Lucifer drinking coffee.
Somehow it got a little darker.
Anyway, I hope you enjoy this story!

Sometimes he felt far too old for this world. He'd watched kingdoms rise and fall; he had dedicated his precious, always scarce time to so many different causes, each of them promising him to cure his aching bones, his sore joints, his collapsing lungs, his raw skin, the decaying of his being.

And every ten years still he drowned in his own blood and woke up in a body foreign to him for at least another year until the suffering would start again and the familiar pain would return.

Lucifer was tired of living but even sicker of dying.

Perhaps that was the reason he had agreed to Samael's offer so easily, not even caring to negotiate the details with him, certainly a dangerous mistake to make when dealing with the King of Time. But Lucifer wanted to be able to take a breath without starting to cough and eat real meals without vomiting.

If he had given this project of Samael more consideration, maybe this situation could have been avoided.

"Their names are Rin and Yukio," Samael said, for once abandoning his foolish demeanor and acting like life was more than a simple game of chess whose outcome he'd predicted before it even started.

Lucifer studied the newborns lying innocently in their crib. If he were younger, say Astaroth's age, he wouldn't believe them to be anything but two human children with pink skin and black hair. Sleeping together like this, curled around each other, they appeared to be far from the tragedy they were sure to become.

"They're not human. What are they?"

He didn't take his eyes of them, wondering why it was so hard to tear himself away from their sight. He wasn't waiting for chaos to come crawling out of the corners, though the chance of that happening was rather high considering they were standing within Samael's home, but still there was a pull drawing him to the twins.

"I don't know," Samael admitted, frowning. "They are from Gehenna but not off Gehenna, not in the way we are."

Lucifer turned to his brother, wincing as his side stung him sharply with what felt like razors. His painkillers were wearing off again, he needed to take his next dose soon if he wanted to get some shut-eye.

"What are they?" He pressed.

"Children."

"Whose, Samael!? Don't play games with me. Not now."

Samael's eyes flashed dangerously but even so, he just laughed drily and didn't hesitate to answer.

"Its, his, Gehenna's, Satan's or whatever name it has decided to go by now. Apparently, the Ego of a world can develop beyond the boundaries of one plain as long as its thirst for more is saturated, which it never will. Demons are never content, we're always starving. These two are 'Plan B' as far as I can tell. They contain the same power, if weaker, within them. That power is sure to grow beyond everything even my seals could control. They are basically Gehenna's failsafe if I can keep it from opening a Gate to Assiah; the perfect vessels."

That plan sounded just mad enough to hail from the world they kept trying to escape.

"We can't let that happen. Why have you allowed them to stay alive?"

Murder usually wasn't Lucifer's first choice of action but already the existence of these two innocent beings risked the safety of Assiah. It would be unwise to let them live and grow up to be Gehenna's perfect puppets.

"Because of all the possibilities these two promise. They are similar to Gehenna in all but one; they are part human. They were born in Assiah! Imagine what we could do with that, Lucifer. The cores of a world in a stable human shape. All we need is for them to grow up ready to use that power."

Samael grinned like a shark, revealing the dangerous predator hidden behind the mask of a trickster.

"What are you planning, Samael?"

"I'll put a new king on Gehenna's throne and you will teach them how to do more with that crown on their heads than to simply show it off. I know you remember the fall and the shaping of Gehenna."

Oh yes, he remembered the burning of his fingers as they dug them into the darkness of nothing in particular; shaping, creating-

"You're cruel, brother," Lucifer said and stepped closer to the crib again. He reached for the fussy twin and lifted him up, gently cradling the babe. "Ruining their lives like that."

Samael snorted. "Like you care about them beyond the possibility that they might be able to relieve you of your pain."

The child calmed down and soon his breathing was even again.

"I never said I had any moral high ground."

He returned the child to his brother and, with one last glance at the two, left the room behind, his legs feeling like they wouldn't carry his weight much longer.