Notes:

The last trailer is here my fellow nerds! Wow these were fun to do.

Who is your favourite Primarch child in this AU and favourite trailer?

Thank you all for the support and comments so far! I didn't expect this idea to take of like it has.

Also, Ruby is autistically smart in this.

Morticia (Ruby Rose) was born to the Primarch Mortarion and his then wife Celestina, on the death world of barbarous in an interesting set of circumstances, chief among them being it was the day the emperor gave Mortarion aid to reach and kill his adoptive farther and the tyrant of Barbarous. The emperor had been interfering in secret to aid and make safe his son.

The second circumstance was when Ruby was born to the "shroud born" tribe and when she cried for the 1st time and her tears hit the floor, it sprouted few patches of fully formed red roses... One of the few untainted plants on the whole planet.

Mortarion and the Emperor rushes down the mountainside to Mortarion's home, they see a look of mourning on all their faces and Mortarion's twin hearts drop in his chest as he runs inside nigh swatting aside his own people in a panic.

He rushes into the midwife's room and saw his only love dead on her bed and the midwife holding his daughter who's crying her eyes out and is pale as a sheet...

Mortarion who was famed for his rage when he was failed in anything, and he stairs down the midwife as if his very gaze could kill her where she stood, causing her to panic and handing the Primarch his child and fleeing into the corner of the room as if that would save her if he decided to kill her.
But when Mortarion held the tiny new-born and looked down into her eyes and the crying died down to one of happy cooing he felt an odd sense of peace fill him and as if her very gaze could calm him...

The 3rd thing about that day was the fact Mortarion's daughter, who was later named Morticia was she had a truly rare trait even the emperor admits was rare and that was the legendary silver eyes, a trait possessed by psychic blanks that allowed them to have utter mastery of their ability and allowed them to use psychic power and by all accounts could operate as completely normal people.

But Morticia was anything but normal, she was a demi Primarch, but was born with an incredible intelligence and it seemed her mind grew quicker than her body did, by the Terran age of 1 she bore an incredible interest in dreadnoughts and when the 14th legion "dusk raiders" and arrived on Barbarous she had all the tech she could want, especially dreadnoughts...

She took a really strong liking to the Contemptor pattern dreadnoughts especially the standard pattern, as she saw it as having nigh infinite upgrade potential, and very quickly set about using the full extent of her station as a demi Primarch to learn everything she could about it, every book and cranny she became very familiar with and could recite everything verbatim and from memory could give a full run down of the whole chassis.

Luckily, she had an unoccupied dreadnought to examine, but also took great care in helping and taking care of the occupied dreadnoughts in the legion to the point a phrase had been made about her form the Terran born troopers "if our gene sire's spawn is missing 1 of two things is true, she's working with our dreadnoughts or she's in his company"

It would seem that Morticia or the "rose of barbarous" due to her tears sprouting roses if they hit bare soil, was one of the few demi Primarchs who fulfilled their intended purpose, to act as a balancing act for their Primarch parent and Mortarion had become more... balanced so to speak.

For a start the legion had mostly escaped from his rather brutal trials, with most of them being lessened or outright scrapped for most of the Terra born astartes, with Morticia having convinced him of their worthiness at having gotten this far without him and had said "imagine what they could do WITH you"

Morticia was only 3 Terran years old when she received her carapace ports and her pure silver coloured armour of the Mk2 pattern, which was modified to be as mobile as possible with Morticia having grown very fond of high speed and thundering strikes with assault marines and a liberal use of dreadnoughts.

But she had done the impossible, over the course of two years with intense effort she had built a human pilotable dreadnought...
Well as human as you can get being a demi Primarch

It was inspired by the earliest proto types of the dreadnoughts and her experience working on them, and with a boundless energy and intelligence had set about designing it. And when it was finished, it stood a full ten meters fall with Morticia having done away with the dreadnoughts typical sarcophagus systems, and subsequently was able to effectively shave 4 meters of hight of the dreadnought design, with the design base being a Contemptor pattern.

When she wished to enter It, the entrance to the war mech was directly underneath the main torso but slightly towards the back, and was large enough to accommodate her in and out of power armour, Morticia had built an extendable ladder for it but often used her powers to hop up into it.
Her favoured weapons were twin Kheres assault cannons, twin fists with chem flamers, or if she could source them, Volkite batteries typically reserved for Deredeo pattern dreadnoughts.

this understandably made her extremely famous and infamous in the legion and imperium and Mechanicum, with many of said tech adepts either begging for the STC she, they assumed MUST have found to pull this off, or demanding she submit herself to trial for tech heresy, with the latter being an extremist sect among the Mechcanicum and when Mortarion had learned of the demands for trial, had ordered well over a hundred astartes to gather them up and put them to death on treason charges.

Morticia however didn't solely use her war mech, she made good use of her power armour and speed even becoming quite skilled at the use of the power scythes her legion and especially the death shroud.

when the reforms to the legion had been finished, Mortarion decided that the 1st grand company to be founded after the 1st 7 in his plans to expand the legion was to be given to Morticia to command and to use as she saw fit within the bounds of the legion's laws.
Morticia wasted no time in creating what was a huge assault company in its own right, all it needed was to get into action to unleash the fury of Barbarous...

One day Morticia who was in her workshop on her strike cruiser the "barbarous rose" working on her war mech, under the watch of her own Tartarus terminator elite formation, the Rose Shroud with a preserved Rose in armoured reliquary's hanging form their breast plates with red cloaks disguising them in the recently dim light. Then the Primarch himself and the Death Shroud guard entered the chamber, spooking the few trusted housecarls and tech adepts working with Morticia.

Without words both they and the rose shroud left the chamber only leaving the royals and the terminator elites behind.
the young demi Primarch takes of her welders helmet off and shook her head free of soot and dust, having spent a full 4 hours performing maintenance on her beloved Iron Rose.

She greets her farther saying "farther, what brings you to my cave"' she said with a jest as without her armour she was hopelessly dwarfed by her farther, being thee shortest royal child by far at her current night of 5ft 2.
The Primarch nods to her, a brief smile from beneath his hood as he knelt down to pet her head "I wished to see your work before we depart for terra, the emperor has called all Primarchs to terra for a family reunion, all of your uncles have been found"

Morticia beamed at this, wiping her face with a cloth "yay!" She nearly belts on impulse before very quickly calming her excitement, as she ran over to a pair of metalic gloves and says "these are experimental control gloves, there meant to try and allow me to give it commands without myself needing to pilot the machine directly, at least to get it to me, without having to exit the battle to come get it, but sadly I haven't been able to find a way to get the connection formed properly, as when I 1st tried it, I nearly snapped major power cable's which were a pain in the arse to fix" she says sadly frustrated setting the gloves down.

Reluctantly Mortarion sent his guard to wait outside waiting until the bulk head doors closed up before responding "I'll make sure to provide you with any relevant information you desire, tell me my dearest daughter wha.." He stops and growls as he heard the thunking boots of Typhon rush into the room, bearing a message with the death shroud following. weapons raised to strike him for his insolence.

Morticia scowled at him, never liking him or his borderline treacherous demeanour and had a very deep-seated disgust to the man as he spoke to his Primarch "my lord, a Greenskin incursion in the next system over, it's a space hulk my lord and its already in orbit of the Agri world in that system."
this has Mortarion fuming and visibly angry, not at the Xenos he now has to deal with, but at being interrupted when talking to his price and joy and was seconds away from murdering Typhon...

"Have the legion prepare to depart at the double... and if you ever interrupt me when I'm speaking to my daughter again, I will have your head"
Morticia grinned to herself at the fact the 1st captain she despised was being bitched out to his face with a childlike glee. she set about cleaning herself and prepping her mech and gear, as Mortarion left without much fuss except for an approving smile at his daughter.

a few months later...

Mortarion and his daughter had arrived on Terra at the same time as Perturabo's iron warriors, and the 15th legion of which he didn't know the name of, both he, his daughter and their respective captains were in their stormbird as it touched down and opened its ramp to the outside world, and they exited to a warm welcome form Jaune of the Luna Wolves alongside his farther Horus Lupercal with the former greeting Morticia.

"You must be the "rose of barbarous" I'm Jaune, Jaune Lupercal a pleasure to meet you" he extends a hand to her, an action partially made awkward by the hight difference inside their armour. Not dissuaded by this Morticia smiled, her red cloak blowing in the cold air "a pleasure to meet you to, I've seen your company record, it's really cool!" The two demi Primarchs depart talking to one another leaving the two Primarchs to speak as brothers.

One the way into the palace the two demi Primarchs come across Lorgar, Kor Phaeron his daughter and Erebus... Morticia had grown to absolutely HATE the entire legion, having not a good thought towards them, but seriously had to TRY to be nice especially during this event.
The Primarch of the 17th legion had moved to greet them, his voice that of a preacher putting on a fatherly voice, which only serves to creep Morticia out even more than his bald tattooed head already does.

"Greetings oh daughter of Barbarous, I am Lorgar of the word bearers." He kneels and brings her right hand which has a ring, which belonged to her mother and kissed it and Morticia, has to deliberately power down her armour to nominal levels to not flinch on impulse, as the only reply she could muster was "likewise" she said ripping her finger hand away as Erebus had moved to make his introduction.
After her said his pleasantries, he moved to kiss her ring as was courteous on Colchis.

But when she looked at him something in her flashed from her eyes and all she could see was a swirling mass of chaotic colours and energies. she recoiled to the point she nearly tipped off the landing pad, if it wasn't for her boot's mag locking her in place. when Erebus went to catch her, her eyes flashed bright white sending him back right into Kor Phaeron nearly taking the two of their feet.

this disturbance has a Custodes Allarus terminator, Horus and Mortarion rushing over to see what had just happened, with Jaune consoling the deeply embarrassed Morticia.
Mortarion angered, asks "what happened?" His tone was a deep rumble, having become extremely protective of his ball of sunshine, and noticing this Lorgar silences his two captains, and silent daughter from speaking saying "just a mere psychic mishap, a misunderstanding, brother Mortarion"
Lorgar goes to apologise to Morticia, but due to her embarrassment at nearly sending two astartes flying has her saying "stay away from me" before using her psychic ability of speed to zoom past all of them even catching the Allarus by surprise at the sheer speed

A few hours into the visit...

Since meeting the men of the 17th legion Morticia has been glued to her father's side not wanting to chase another scene her anxiety flaring up to the point she was tempted to teleport up to her strike cruiser and work on her war plate.

As her dad is mid conversation with his brother Horus Morticia sees the emperor for the 1st time and with a burst of excitement, she uses her power to launch herself forwards him even out matching the advanced sight of even the custodes.

She had come out of her speed right into a warm hug as everyone present watches on in horror shock and amusement, and the reaper of Barbarous looks like he's about to die of pure embarrassment but, much to everyone's shock, the master of mankind despite not being in his armour, is able to pick up Morticia in her power armour. And he cradles her almost as she says "I heard you have Custode's dreadnoughts! Can I see them?!"

the emperor let's out a hearty chuckle as he holds her and responds "how could I refuse such a kind request" he then asks everyone to take up their seats in the dining hall, as he detours to the armoury of the palace with the adorable rose of barbarous in his arms.

Once past the huge titanic bulk head armoured door flanked by two custodian wardens, the emperor sets down his grandchild as the lights in the chamber switch on to reveal a few dreadnoughts of the custodes, sub types of Contemptor with the Tellermon's being in the other armoury.
Now on the floor it takes all her might to not rush right up to the dreadnought and risk waking its occupant.

"I found the STC for the Achilius pattern not to long after the unification of the soul system, what makes this particular type unique, is its weapon"
He uses his psychic might to pull the Achilius's weapon of the walls, and levitates it in front of Morticia, who is starring with a sense of childlike wonder as she circles around it

"a guardian spear but it's ranged weapon is a Laz cannon? I didn't know you could build dreadnoughts this agile... The power system and the quality of the tech in its hands, must be a lot more advanced than the standard pattern by leaps of magnitude, the joints must be a lot stronger to compensate for the increased stress as a result of the new range of movement."

she says nerding out as if she had a note pad out for several minutes before she remembers she's with the emperor, and she stops blushing a bit saying "forgive me, I get lost in all the excitement" the emperor sets the spear back onto the wall next to the dreadnought chuckling "it's fine young one, I used to be much the same in my young days, close your eyes I have a gift"

she squeaks with excitement as she complies, and with that the emperor manifests his personal copy of the Achillus pattern dreadnoughts STC fragment, being one of few he possessed and with his might makes a second one. after some truly hard amount of effort he finishes the copying and hands it to her saying "now open"

once she does, she gasps "wow... is this?" "Yes, it is, it is yours to keep and use as you see fit under the condition you and you alone are the one to use it, consider it a gift from a grandfather to his grandchild, come we have a feast to attend to" he extends his hand to her and the two depart with the dreadnought using his vox to say to himself "you've changed master of man"

Years later...

Over the next few years, the great crusade continued with Morticia and Mortarion's Death Guard dealing a bloody tally against the imperium's enemies, especially Xenos species being both Primarch and royal child preferred targets.

However, as the years progressed Mortarion had grown very fond of his brother's Horus's company with Morticia getting on famously well with Vulkan, Sanguinius and even Konrad Curze and their respective daughters. And thanks to the suggestions and spending time with the 1st two, had picked up key skills and engineering and with the STC fragment was able to build Achilius pattern fists for her Iron Rose which allowed a drastically better range of movement.

And then Davin happened...

Jaune a friend of hers and the son of Horus Lupercal the war master, had fallen victim to a truly horrifying poison and in his grief, Horus had murdered Erebus of the Word Bearers, something Morticia admits to herself was deserved as, Erebus was a cancer in every fleet he joined.
But over the years she had noticed the presence of a warrior's lodge emerging and the Terrans and Barbarans had started to despise each other more and more openly which admittedly was a problem but it had only grown worse. And that was taking the recovery of the Ragdang Xenocides.

Her farther Mortarion and become distant, angry, spiteful to his men, during that time even Morticia had to TRY and get just an audience with him whereas before she could sneeze the wrong way and he'd come straight to her...

It was as if he had been told something or had experienced something that left its mark upon him.

And then came Isstvan...

A few days after the massacres...

It was a bloody campaign indeed; it was requiring multiple legions she thought to herself as she was inside of her war plate equipped in its first configuration, as she's stood on the drop deck of her cruiser the "barbarous rose" alongside her rose shroud terminator elites when suddenly she gets a panicked report form her astorpath chamber "we're under attack...t..ter..m..antors..." Ruby despite not hearing it right knew with her advanced intelligence, understood what he said and took off running across the drop deck her guards following her.

Her 1st captain, named Alastor, struggled to keep pace with the jogging war much as its feet thundered into the deck "my lady what is wrong"
Is it received a distress call, our astropath is under attack! "

Once they had gotten there, they saw members of the 1st grand company, a death shroud terminator and multiple standard power armoured astartes, all beating down on the doors of the astropathic chamber. Seeing this Morticia uses her of hand and prepares to use her chem flamer built into the palm and barks "stand down! stand down! Explain yourselves!"

The group of 10 astartes about turn to see their Primarchs daughter and her 5 rose shroud elites and the leader, the death shroud speaks "there are traitors and criminals hiding within the chamber my lady, your farther has ordered their arrest"
"If this is an arrest, then why do your bare weapons for full combat operations? " She spits back igniting her flamer, and hopes she doesn't have to use it as she couldn't care to think she'd have to kill astartes especially those of her legion...

Then she hears about a dozen power armoured foot falls behind her, and tapping at the console in her pilot's seat she uses the rear facing camera to look and see their holding Laz cannons... At this point she realises she's been betrayed and spins around, dousing the hallway in burning chemical fire incinerating the 1st 6 instantly as they died screaming in agony...

The rose shroud doesn't need orders they fall upon the astartes in front of them, their bolter rifles not proving effective against the shielded and incredibly swift Tartarus terminators, with the death shroud member being the last one standing and severely wounded after levels chaotic minutes of melee...

With the hallways aflame in chem fire and with several Laz cannon blasts on her creamy white chassis she turns to her guard and barks "we don't know how deep this betrayal goes...order every ship that is a part of my grand company, and order them back to Barbarous, me and Alastor will drag this traitor before the Primarch to see justice." They nod as damage control out if he fires with shocked faces and the orders are carried out...

Later on, the Terminus Est...

Morticia, the death shroud traitor and a few select rose shroud all exit the storm bird to a waiting Mortarion, and the high command with lights blaring as they were trying to warp jump but found themselves unable to.
Once he sees the Laz cannon marks on her chassis he's enraged and asks "WHO. DID. THIS."

Morticia drags the traitor death shroud across the deck and slammed him before her farther "he alongside 22 others had conspired to kill me and kill my ships Astrooapth, I have reason to assume this has already happened or is ongoing throughout the fleet, there is a conspiracy"
Mortarion enraged and is already shaken up form what he had just done to his legion and the other's on Isstvan uses his scythe to decapitate the death shroud terminator and says "we will deal with this once we're back at barbarous... Are you well?"

he asks in a way he hasn't used since the triumph on Ullanor and Morticia responds "I'm fine, just disgusted at what I had to do"
Typhon realised his plan for his dark God Nurgle was becoming dangerously close to utter failure suggests "my lord, given the warp storm and the difficulties navigating it we've been having, I suggest our librarians help guide the atropaths for our journey until replacements are found and the storm clears" Mortarion reluctantly agrees and nods as he walks up to his daughter's dreadnought.

After twenty some minutes of the two royals talking Morticia notices something is really wrong despite having never been to at good social situations. Her farther looks like he's on the verge of a breakdown any second, as if he's hiding a dark secret from her and judging by the look on faces, she figured something terrible had just happened she just hoped more brothers didn't turn on brothers or somehting worse.

And then came the warp jump...

Once in the warp, a dark green fog had settled on not just the hangar, but the rest of the ship and even the fleet, at 1st Morticia thought it was a wired quirk of the warp, having never understood it fully despite her own company librarians attempts to teach her but once the coughing and mutations started? the true horror began...

Many dozens of proud legionaries were throwing up sick disgusting black and yellow bile, many dozen more had started rapidly mutating large puss filled boils all over their groupies which were dripping their armour asunder...
Morticia unleashed her chem flamers when several astartes had attacked her whilst mutating, burning them, which made the effect of what where a happening so much worse...

Morticia was flying into a blind panic as her, war plate that she named "Iron Rose" was screaming for her to get the fuck out of there and her hermetic seals would not last very long as it was being eaten and decayed and her joints were sizing up.

Her panic was made worse by what was happening to Mortarion... He was throwing up huge amounts of puke... his armour was buckling and bending out of shape, and his back was exposed out of his armour and seem to have something building beneath the surface of his flesh...

And typhon walks back into the deck chuckling, as dozens of flies and bloated fat maggots wriggle and slither out of his broken breast plate, he watches as Mortarion, despite resisting Nurgle's gifts was FANATICALLY defending his daughter to the bitter end. He knew Mortarion would never raise a hand or weapon against her and so, he sicked the plague bearers upon her as he saw Morticia as nothing more than a hinderance.

Typhus now watched with glee, as one of the Lord of disease chosen demons toppled the mech onto its back and he could hear its little pilot screaming in horror, as the mech swung its power scythe wildly and fired its chem flames until they ran dry.

The cackling and sputtering, 1st captain strode over the decaying corpse of one of Morticia's rose shroud guardians who died in Morticia's defence, stops beside the near dead Primarch, who had just strangled a tainted death shroud to death and says, with maggots pouring out of his mouth starring at the horrified Morticia and says "all you have to do is accept the great grandfather's gifts, and your little spawn will be spared and judging by that look she's giving you, she's begging you to take it"

Morticia sees Mortarion, her farther, look up at her with sad eyes as he's seconds form accepting and something inside her snaps...

Her eyes crackle with a power not seen since before she was born as she SCREAMED out in anger, as the blinding white light filled the hangar, and seemed to banish the very warp itself for a time casting demons back into the realm of Nurgle, and killing infected death guard.

the crying weeping Morticia who was burning up from the inside form the use of her power, scooped up her farther and with a thundering roar smashed the armoured window and leapt into the raw tide of the immaterium, losing her dreadnought power scythe in the process...

After a few moments and only being protected by sheer raw power of her psychic banishment ability both she and her dying farther are spat out into the atmosphere and sent them crashing into the soil of an island inhabited by young adults and the demi Primarch, Yang of the blood angels...

Raven, Qrow, Summer, Taiyang and Yang come rushing out of their house and see the severely battered ten-meter tall mech, holding a horrifyingly wounded and battered large super human with the soil and the very air around them was thick with ethereal heat and sadness.

The gas masked helmeted mech uses one of its hands to pull its helmet away revealing the traumatised and crying bloodshot eyes little girl who upon being recognised by both Yang and Qrow they feel fear grips them...

Summer through a fear-soaked Sutter asks "Yang...Qrow? what the fuck is that?"
Qrow answers "that's Morticia, child of Mortarion and that dying man in her arms is Mortarion himself, one of the Primarchs I told you about... and her mother..."

Raven knowing just how tough a Primarch is 1st hand, is sick to her core at seeing a Primarch on the brink of death and says " I'd never thought I'd see the day... " Yang out of fear for a friend runs over to Morticia and Mortarion but is stopped by Qrow already knowing the Primarch is doomed just by sight alone.

Mortarion barley masters the strength to rip his hood away, to reveal his dirty blonde to pale white-haired face to his daughter, and with blood pouring down from his wounds where his mutations once were, he weakly says "my scythe... pass it to me... please..." Morticia complies through mournful sobs as the realisation of what's happening to him hits her.

The Primarch clutches his favoured weapon in hand and looks at it smiling "the day you were born... I won this scythe killing the tyrant of Barbarous... I did so with the strength and knowledge that I'd return victorious to a loving wife and sweet baby girl... the day you were born... the 1st tear you shed spawned a patch of rosses... I preserved so the 1st one as to keep a memory of it... it's on my hip pass it to me..."

she passes it to him and he then says "I'm dying Morticia... please give Iron Rose a rest... I want to hold you close..." Taking a few steps back she exits Iron Rose and rushes up to him, her power armour helmet is hanging of her hip.

Kneeling beside him, helping to prop him up as the two wait out the last few moments together when he speaks "help me face the dawn... I have something to tell you..." With a great struggle she has him moved so that they both can watch the sun rise holding each other tight...

"Your mother, Catalina... wanted... to name you Ruby... I was a fool to have chosen Morticia... listen to me Ruby" he says switching to that name " I couldn't have been prouder of you... I didn't deserve you... Barbarous was more deserving of you... "

He's stopped short by a loud wet sputtering cough before he resumes "let these words by my last to you my Rose... no matter what happens, no matter what I've done, you were always my reason to keep going... I know your scared... please no matter what happens...stay... Strong... and nothing... will assail... you..." As the very last words leave his lips, Mortarion, primarch of the 14th legion dies in his daughter Ruby's arms on the death world of remnant on the 31st of May millennia 31...

To be continued...

Notes:

What did you guys think of this AU of Mortarion? Is he more likeable than his cannon counterpart?

I had to take an emotional clam down break twice writing the last quarter of this chapter.