In the Age of Dark Technology, humanity introduced xenos technology into its own science to further enhance efficiency, and even incorporated alien genes into the human genome, creating a vast army of genetically modified humans.
The result was that by the end of the Age of Strife and into the era of 30K, pure-blooded humans had nearly gone extinct.
Only perpetuals such as the Emperor, who had survived since before the Dark Age of Technology, or a handful of isolated colonies that had little or no contact with mainstream human civilization, still possessed untainted human genetics. All others were mongrels at the genetic level. The genetic similarity between two random "humans" might well have been lower than that between a man of the M3 era and a common housefly.
In such a society, the birth of mutants was nothing unusual. What was remarkable was that most humans still retained a vaguely human form at all.
Yet it was precisely thanks to those alien genes that the hive underdwellers could survive in such a hostile environment, natural selection at work.
"The bodies are dealt with."
Curze, now grown into a youth, returned to the room. He had just killed a few Bloodclaw gangers and seized their shelter.
The corpses were tossed outside. Scavengers would soon strip them clean; nothing would remain.
Caelan asked, "How much farther do we need to go?"
Philly curled up in the corner.
"This is Bloodclaw turf now," she explained nervously. "The ones you killed were their patrol. I don't know where the lift is… I've never been there."
She spoke timidly, terrified of angering Caelan.
"It's fine. This is far enough. We'll find the rest ourselves."
Caelan understood. She was just a scavenger. Guiding them into Bloodclaw territory was already the limit of her usefulness. The elevators to the upper levels would be tightly guarded; if she had ever seen one, she would not be alive now.
"Are you going up to the upper levels?" she asked softly.
Curze glanced at Caelan. He went where Caelan went.
"I'm not exactly a man of plans," Caelan said. "First, we find the elevator, then we'll see."
"Bloodclaws have numbers. They have guns." Philly warned.
"I'm good at killing," Curze replied calmly.
"I… I know someone," Philly hesitated. "She might know how to reach the lift."
"Why didn't you say that earlier?" Curze stared at her, making her shrink in fear.
She looked at Caelan, then relaxed a little. Pulling away her heavy scarf, she revealed pale skin… and patches of bluish scales along her neck.
"I'm a mutant," she admitted.
Caelan asked, "And the one you know?"
"She isn't. But she takes in many mutants."
"So you worried we'd hate you, or kill them?"
Philly nodded.
"Then why tell us now?" Curze asked bluntly.
"…Because I think you're good people. You never killed him."
She meant the boy outside, who had been trailing them at a distance for two days, never coming close, only following.
"Curze, bring him in," Caelan ordered.
Curze nodded and went out, returning shortly with the boy.
The child's eyes were wide with fear. He stammered nervously, "I-I mean no harm, I was just passing by."
"What's your name?" Caelan asked.
"Ben."
"Have you eaten?"
Ben froze, dumbfounded.
"Give him a corpse-starch ration."
Curze tossed one over. Ben caught it with both hands, muttering a quiet "thank you."
"Tell me," Caelan asked Philly and Curze, "am I a good man?"
Both nodded.
Caelan raised his scrap rifle and fired at Ben. The boy dropped instantly, motionless.
"And now?" Caelan asked.
Philly stared in shock, her eyes wide with fear and confusion. Curze, however, still nodded.
Caelan shook his head. "Don't trust so easily. Sometimes kindness is just a mask."
Curze nodded again. He had the sight, prophecy revealed all.
"Remember this, Curze," Caelan said. "Of all virtues, filial piety comes first, judge the heart, not the deed; by deeds alone, the poor seem unfilial. Of all sins, lust leads the way, judge the deed, not the heart; by hearts alone, none are without flaw. Do you understand?"
Curze nodded, as always.
"I do. It means, don't condemn people for things that haven't yet happened."
"Get up."
Caelan nudged the boy with his boot.
Ben wolfed down the corpse-starch, then scrambled upright.
The shot had missed him, only grazing his ear and striking the wall. His fall had been instinct.
Realizing he was alive, he resumed eating. In the underhive, you never knew if there would be another meal, better to die full than hungry.
"Full?" Caelan asked.
Ben nodded, though he had never truly been full in his life. Any food at all was a blessing.
"Show me your hands."
Ben hesitated only a moment before revealing them. From his sleeves unfurled long, folded tendrils, twice the length of human arms, longer than his own height.
"Give him another," Caelan told Curze.
Curze handed over another ration. Ben thanked him, accepting it with his tentacle.
But the instant Curze's fingers brushed the tendril, his body froze.
He saw the boy's future. He saw a towering warrior clad in blue-black ceramite, kneeling among countless others in identical armor.
That warrior bore no resemblance to the child before him, but Curze knew it was Ben.
"What did you see?" Caelan asked.
"I saw him in armor," Curze said slowly. "He was huge… over two meters tall."
"Then he'll be your son," Caelan declared. "That was worth saving."
"How old are you?" Caelan asked Ben.
The boy looked lost. In the underhive, age meant nothing. Days blurred into the single goal of survival.
Still, Ben looked around seven or eight, though malnutrition meant he was likely older, at least ten.
Astartes implantation required candidates aged twelve to sixteen. Which meant the Imperial fleets would arrive at Nostramo within six years.
Canon said the Emperor found Curze decades later. The timeline was shifting.
"Son?"
The word made Curze pause. He knew what it meant. He was the son. Caelan was his father, he cared for him, taught him.
Now he too would have a son? To raise? To teach?
Impossible.
Curze gave up on the thought, he didn't know how.
From the corner, Philly whispered timidly, "Then… can I be your daughter?"
All three looked at her. Blushing, she stammered, "I mean, I can't be much older than him…"
Caelan shook his head. "Astartes are only male. No chance for you. Blame the Emperor, he never made female Primarchs."
"Oh." Philly wasn't too disappointed. She hadn't really wanted to be Curze's daughter anyway.