Solution

When Emperor used the Primarchs as the blueprint to create the Gene-seed, the characteristics of each Legion were already determined, along with their destined flaws.

Genetic engineering is a profound discipline; even Emperor, who disregarded science, had to adhere to certain fundamental laws. To gain something, one must make sacrifices.

Take, for instance, the Gene-seed of the XV Legion, the Thousand Sons, currently in the hands of Hogg. Because the progenitor is Magnus, the Gene-seed of the Thousand Sons was destined to cultivate Space Marines with enhanced psychic abilities; this was set from the very beginning.

However, having the talent for psychic mastery means one must endure the corruption of the Warp, much like how one gets wet when catching fish in the sea.

After the first batch of Thousand Sons warriors was formed, they began to develop their psychic powers autonomously. Yet, as this progressed, a terrifying and uncontrollable degenerative mutation began to spread.

This strange affliction, known as the Flesh Change, tormented the Thousand Sons. Those Space Marines who suffered severe mutations could only be preserved within a Stasis Field.

In the laboratory of the Blacklight, two Primarchs—one large, one small—discussed treatment plans while facing a Thousand Sons warrior in a nearby Stasis Field who no longer resembled a human.

Magnus had once attempted to fuse so-called Spiritlings into the bodies of the Space Marines, hoping that flesh adapted to psychic energy would develop habitual antibodies against low-level psychic phenomena, essentially a form of alternative desensitization training.

But since the so-called Spiritlings had been confirmed to be daemons, that method was declared a failure, leaving Magnus with no choice but to turn his gaze toward Hogg.

"It seems my method is useless, so I can only see what solutions you have."

After carefully studying Magnus's plan, Hogg did not jump to a conclusion. Instead, he examined the Thousand Sons warrior, who had mutated severely enough to grow arthropod limbs and redundant organs. Portions of tissue that did not affect vital life functions were excised for laboratory analysis.

High-concentration nutrient solution was injected into the excised tissue of the Thousand Sons, and instruments recorded the changes in the tissue samples every 30 seconds.

Based on the tests, Hogg discovered that this group of highly mutated flesh tissue had an excessively high adaptability to psychic energy; they were essentially Warp entities existing in the material world.

Long-term use of psychic powers, coupled with the scars of war, caused wounds that should have healed stably to mutate into tissue more conducive to the flow of psychic energy. The evidence was that the more severely mutated the Space Marine, the more powerful their use of psychic energy became.

But here was the problem: other Legions had their own psykers, so why hadn't they developed such deformities? There had to be a distinction.

After sharing this result with Magnus, the two began to search for a control group.

Soon, several psykers belonging to different Legions were brought to the laboratory for analysis and examination, including those from the Space Wolves, Imperial Fists, and Blackwatch.

Comparing the data of the psykers from different Legions, Hogg confirmed that the issue lay with the Gene-seed.

After extracting the Gene-seed from the mutated Thousand Sons, the new results were used for various stimulation experiments.

But anyone who has worked in a biological laboratory knows that control experiments are the most troublesome; any number of interfering factors can disrupt the progress of the experiment.

After 7,128 sets of control experiments and nearly a month of time, Hogg spotted a clue in a specific set of data.

In this set of experiments, the data for the Thousand Sons became abnormally prominent—the Gene-seed synthesis experiment.

If humans reproduce sexually, then the reproduction of Space Marine Gene-seeds is more akin to asexual reproduction. Once implanted into the body, the Gene-seed synthesizes within the host after absorbing sufficient nutrients.

During synthesis, the Gene-seed records the combat experience of the host while slowly absorbing Warp energy. This faint amount of energy is generally not enough to corrupt a nascent seed.

However, comparing this to the data of other Legions during Gene-seed synthesis, the rate at which the Thousand Sons' Gene-seed absorbed Warp energy was dozens of times higher than that of the other Legions.

This abnormal level of absorption was recorded from the very moment the seed was created, causing the implanted Space Marines to develop a morbid craving for psychic energy.

Coupled with the Thousand Sons' combat style, where every member was a psychic caster, the highly activated psychic energy caused the flesh to mutate, while simultaneously increasing the craving for the use and absorption of psychic power.

Having identified the root of the problem, Hogg explained his treatment plan to Magnus:

"Magnus, I have two solutions, and you can choose one. First, the Thousand Sons warriors must stop using psychic powers from now on. Once they are highly mutated, there is basically no saving them; as long as they fall into this vicious cycle, it is a dead end."

This plan was immediately ignored by Magnus. Although he no longer blindly worshipped the power of the Warp, it was undeniably useful.

"I choose the second one. The Thousand Sons cannot lose the power of the Warp," Magnus said excitedly.

"Then we can only suppress the intake rate of psychic energy during the synthesis of the Gene-seed, and at the same time, create a new batch of Gene-seeds using your genome. It just so happens that I possess this technology."

Soon, a set of Blackstone devices was transported into the laboratory. Looking at the alien construct flickering with green light, Magnus was a bit bewildered.

"What is this? Imperium has strictly forbidden the use of xenos technology."

"Oh, give it a rest. I've been using this stuff openly for a long time, and Emperor hasn't said anything, has he?"

Watching Magnus being pedantic, Hogg realized for the first time that the "Little Pony" was actually this naive.

"There are no 'buts.' Everyone is using it; you just don't know it. Do you believe that other Legions have even more alien trinkets hidden away than I do?

Honestly, I'm even more convinced that you're just a 'sunburned Ogryn.' Not to mention anything else, look at your own transformed state—you have the nerve to lecture me about using xenos technology?

Forget it! As Primarchs, we were never clean to begin with. Our very existence is the greatest blasphemy against the Imperial Truth. Without the xenos technology you speak of, all these warriors would just be waiting to die."

Magnus was left speechless by Hogg's words, his entire demeanor wilting as he could only watch the device being installed.

Seeing Magnus standing there like a child being punished for a mistake, Hogg, who knew the outcome, looked at the thoroughly mutated Thousand Sons warrior in the field and managed to suppress his own temperament for once.

"Little Pony! If you want them to end their lives with dignity, you must take responsibility. I will ask you one last time: do you accept this plan?"

Hearing Hogg's words, Magnus, as if realizing something, nodded with difficulty.

The highly mutated Thousand Sons warrior was placed into the field of the Blackstone device, the emerald electric light signaling that the apparatus was running steadily. The isolated Warp fluctuations allowed the suffering Thousand Sons warrior to relax.

After a period of time, the swaying, deformed tissue began to atrophy. Hogg, holding a scalpel, cleared it away bit by bit, leaving behind a basic human form.

Seeing that it was indeed effective, Magnus breathed a sigh of relief. As long as he could save his sons' lives, he didn't care if it was xenos technology. If anyone dared to say this device was disloyal, the Thousand Sons Legion would make them choose their words very carefully.

Dropping the scalpel, Hogg pulled out a massive needle.

"Come here. I need to collect your genetic samples to recreate a batch of Gene-seeds. It's a good thing Emperor didn't keep secrets and instilled the technology for creating Gene-seeds in me back then."

Bright red blood was drawn from Magnus's body, filling several large culture tanks.

Having finally obtained an opportunity to collect samples from another Primarch, Hogg did not hold back, filling an entire container with blood—nearly draining the "Little Pony" to death.

Just as Magnus believed the Flesh Change within the Legion could be completely resolved, he suddenly discovered that the son lying on the operating table had lost his life.

Panicked, Magnus hurriedly pulled the needles from his body, grabbed Hogg, who was drawing blood, and shouted an interrogation:

"Damn it! Tell me what happened to him—he was fine just a moment ago, so why is he dead now?"

Swatting away the hand pressed against him, Hogg, having no patience for him, kicked Magnus straight to the ground.

"Didn't I tell you! Those with high-level mutations have only one path, which is death. I have already given him a dignified end so he no longer has to endure the agony of deformity. What are you still hoping for?"