A New Heresy (inspired by earlier discussion)
Inquisitor Greyfax calmly looked down at the heretic she just executed with her condemnor boltgun: another Space Marine corrupted by the heresy that was occurring in the thrice-cursed Slawkenberg warzone, otherwise known as Cain's Sector to his fanatical followers. It seems not even the new Primaris Space Marines were immune to the so called "feminine charm" of Cain's newest armed forces.
Greyfax spat at the thought of that damned heretic. It was not enough that his growing rebellion had forced a war on both sides of the galaxy against the forces of Chaos, allowing Abaddon to cause the Cicatrix Maledicutm, he also had the gall to actually be smart enough to keep his heretics in line and grow his rebellion to new heights rather than spread out of control like the Warmaster. Worse, while other Chaos lords reeled from the Indomitus Crusade and the new Primaris Space Marines pushing back, Cain had devised his own genetically enhanced warriors.
When the Indomitus Crusade arrived in Cain's Sector to bring the planets back into the Imperial fold, their ships were boarded by what appeared to be Chaos Space Marines, abeit ones that wore Cain's symbol rather than whatever warband they were original a part of. It was initially thought Cain made a deal with various warbands beforehand to protect his holdings. The actual answer was far more socking and had drastic effects on the Imperium as a whole.
All ships received a vox transmission form the leader of this new force that they were to surrender and to the Adeptus Astartes an opportunity for something away from war. All Adeptus Astartes were ready to deny the heretic's words until the the heretic removed her helmet, revealing the face of a woman with blonde hair and green eyes. The heretic stated that she was Lieutenant Mira DuPanya of Cain's Angels, and proof of the Imperium's lies. She offered the Space Marines a life not bound purely by honor or warfare. Greyfax spat as she recalled how half of the Astartes look ready to join the heretic then and there. It seemed for all the training and indoctrination Space Marines received as training, they never expected to come across anything like this. Only Roboute Guilliman immediately dismissed her and arranged a counterattack, abeit one done with less than efficient means, as though Lieutenant Mira was repelled and her company forced to retreat, she did so with no losses on her side. Worse, it seemed that a number of Marines had "vanished" during the foe's retreat. The Crusade Fleet was reeling by this news that all plans to liberate the sector were put on hold until this situation could be addressed properly.
From there, word had spread fast and soon the Ordo Hereticus had to deal with the danger of many Chapters abandoning their duty. Greyfax could only thank that this heresy was still in Imperium Sanctus as despite the fast word, it also meant the Imperium could and will respond to this latest heresy. At that though, Greyfax sent up a vox to Guilliman to inform him of another heretic executed.
"Thank you, Greyfax. It appears I will need to make more addendums to the Codex Astartes to better indoctrinate us against this new threat."
"Indeed, my lord."
"Still, I don't understand. Why would these "Female marines" cause such a stir among my sons? Especially when biologically speaking, there's far less risk when dating a Elda-" Greyfax immediately cut off her vox and sighed. No, no she was not going to listen to another one of those rants today. Not without several decanters of amnesec on hand.
"And that's the situation, Commander Cain." Lieutenant Mira stated, saluting.
With all the effort I could muster not to scream, I nodded. "Good work, lieutenant. The Crusade should be blunted with the offering we have made to the Adeptus Astartes. While I doubt many will accept an alternative to their lifestyle, we still should give them a chance." With that I turned off the vox and quietly contemplated the latest way I had managed to accidentally screw over the Emperor yet again.
It had all started with that damned Panacea STC. Despite me giving the original to Amberly, the damned fact I had it in the first place spread like wildfire, attracting the attention of numerous bands who thought I had more. By far the worst person to hear of this was none other than the vile Fabius Bile himself. The Clone Lord himself came and, despite my fear of being added to lengthen his cloak of human skin, instead offered a trade. A copy of the STC in exchange for a stock of preserved uncorrupted geneseed, which he happily explained to me to function off. Eager to get such a madman off the planet lest he start experimenting on the local populace (who I was sure would blame me for allowing such experiments to begin with) I agreed had soon had a stockpile of weird genetic material I decided to not touch. However, it was then that the Handmaidens, under Emili, gave me an offer I knew I couldn't refuse.
The Daemon Princess said to use this new gift to create our own Space Marines, loyal to us. I would have pointed out that this didn't stop the Horus Heresy but everyone else was far too eager to see such warriors under our control, rather than having to deal with Warbands of varying sanity. In an attempt to turn this into a failure, I suggested using women over men, as to "show the Imperium that such divides were more social than biological" or some claptrap I cannot remember. What I wasn't expecting was the damn thing to work, nor for Fabius Bile to like the idea so much he left one of his apprentices to oversee the process. Before I knew what was happening, I had a nearly demi-company of genetically powered women who would follow my word up until the great betrayal would inevitably happen, with work being done to create more.
It was at that point I had received word of the Indomitus Crusade had arrived on our doorstep, with nothing less than the Ultramaine Primarch himself at the flagship. Thinking at the very least, I could get rid of this heresy, I ordered our new Demi-Company to board the ship and discreetly reveal their presence to the Astartes with an offer before retreating. However, instead of slaying the heretics where they stood, many of the Astartes had joined our cause. Apparently the idea of a genetically enhanced warrior woman was appealing to them in ways a normal human female wasn't. The inicdent was so alarming that the Indomitus Crusade outright retreated, adding another victory to my unwanted lap.
The most alarming part however, was the idea that I might have caused the extinction for every normal human being. If these Space Marines were biologically capable of children, then humanity was essentially on a ticking timebomb. We would be replaced. The thought stayed with me in fear as I contemplated my options at this new predicament.
Note: I know the Astartes probably wouldn't fall that quickly nor act like shy adolesnce in "real" canon but...crackfic is my excuse.