Omni Legion

Founding
Astartes of the Omni Legion are quiet and stern warriors who have grown to embrace their roles as weapons of the Imperium. Tasked with taking to battlefields and slaying all who stand in their paths they do so as silent war machines. Dozens of worlds would either surrender to or attempt to fight these Astartes who were like automatons, though it was noted that some Astartes within the Legion would spare those who surrendered and aid those who were injured in the aftermath. This would form the opinion from other Legions that their bark is worse than their bite. Their bite being the explosive discharge of a bolter.

After the Chapter was founded by the Emperor they were instructed to go forth using many weapons and technology provided by the Mechanicus, their tactics made use of many weapons not even seen by the Imperium yet. Used to test some weapons to ensure they were safe. Despite their numbers being lower than some of the other Legions and their role being made to be a roaming attack hound many worlds would fall under their control with death tolls within the millions within months to weeks.

Reuniting with the Primarch
The 2nd Formation's fleet arrived in orbit of the world Roisigma as the other 4 completed their role in crushing any remaining resistance on the nearby world of "Roidelta". Once there there was high readings of energy on the planet surface which they quickly reported to the rest of the Imperial navy. Receiving permission to go down to the planet surface they did so, not expecting the Emperor himself to begin making way.

Upon the Ice World, Nero quickly discovered camps of slaughtered Drukhari. More as they traveled in their Rhinos they would find the camps in ruins, many cages torn apart and the Xenos smashed and blown apart. They'd spend a month tracking whoever did this, there had to be a militia on this world that was actually hunting and killing the Xenos. Travel on the world was difficult with temperatures that could reach far beyond the human limit, as Astartes they were fine but their concern was losing communications with the rest of their forces and their equipment breaking down. After just over a month on the world Nero and his Veterans discovered their path led them to a cave. Leaving with his own Honour Guards and few men he left the bulk of his forces behind to watch over the Rhinos.

They walked through the blackened ice tunnels, the idea that people would traverse these would get even crazier the longer they walked. Though they soon would hear the distant sounds of metal and voices. Nero saw a light ahead, it was an entrance which the Astartes could barely fit through. As they did the sight was a shock to Nero as he could only stare in awe.

Deep within the mountain and far under the ground they found it, the underground city of "Broken Saber", the remains of an ancient Terran ship was buried under the surface of the world. The entire thing was retrofitted to house thousands of humans, the bulk of the ship must have gone for kilometers out of the sight of the Astartes who could only see the entry. Before them stood a large and sturdy wall created from external panels from the ship they dwelled within. Armed guards along the top of this wall demanded the Astartes identify themselves, Nero stood forward and did just that. Nero was welcome to enter but at the request that the remaining Astartes waiting outside, wishing to discover the identity of these people and perhaps how it was they survived he did just that.

Nero found the people of Broken Saber had managed to use the heat from equipment intended for mining to create water from the ice around them, because the tools had deteriorated over the millennia they couldn't vaporize the water but it was enough to melt said ice. Many animals from the surface had been taken underground and bred for the purpose of producing meat to consume. Nero requested to meet with their leader. After some delay with these people questioning if they should they eventually determined that it should be fine. Claiming he and his warriors had returned home mere days earlier and would be leaving soon.

Far within the ship Nero was led to a lab, it was in good condition considering how old the ship was. He spotted stasis pods off to one side of the room, dozens of them. Before he could ask he was addressed by a booming voice, something about that voice sent a shiver throughout his body. Something he only felt in the presence of the Emperor himself. Nero looked above him and was stricken with awe. A man that could tower over Astartes was above him, despite the larger size of the Omni Legion's Astartes he was still much larger than him. Nero fought the urge to fall to one knee even though he couldn't see the man's face as he descended down to speak to the Grand Captain. The man donned in armour that seemed to be a mix of plate and thick fabric, a helmet covered by a dark hood that obstructed the finer details of the mask. The man called himself, "Vilhelm Dotharl, Guardian of Broken Saber and its people." Upon these words everyone in the room stopped and turned to face the doorway which worked as a perfect frame to display the golden form of the Emperor of mankind who stood observing everything himself.

It’s not known exactly what transpired but Vilhelm left the cave with the Emperor and rejoined his waiting sons. Taking in the sight of their armour and weapons he took his helmet off to reveal his face as the clouds that covered the world would begin to part and the winds would die down for only mere minutes. He looked over his sons who also removed their helms out of respect to their Gene Father before taking to one knee. Returning to Terra was quite the journey for Vilhelm as he was fascinated by the technology that surrounded him. His interactions with the Mechanicus were of great curiosity as he wanted to learn much about them. Vilhelm would quickly join his sons to the front lines where he’d enter battle himself in a modified version of his own power armour and he wielded a power sword he would name “Niphilim Fang”. Vilhelm's hope would be that his father the Emperor would be able to save his adoptive mother’s life.

Legion Organisation
The Legion’s overall size is 128,000 Astartes with it being divided into 5 Formations of 25,600 to overwhelm the enemy with forces that strike at different times and locations. While most of the time the entire Legion will stay together sometimes they were divide their forces under the command of Grand Captains and their own four Grand Lieutenants. 4 Sub-Formations of 6400 make up a single Formation and each of these have their own Captains and Lieutenants in command.

Legion Combat Doctrine
Long ranged combat and overwhelming numbers are the Omni Legion’s strongest aspect but their use of collecting enemy intel and using it to make organized attacks on vital enemy compounds or facilities with small strike teams. Few Assault squads are in the Omni legion so the majority of close range combat specialists are Veterans or Dreadnoughts.

The most common tactic that the Legion will use is striking foes with a wave of Deathstorm drop pods before the second wave comes, this one containing most of their forces while the rest ride down to the planet surface in Stormbirds. Once touching down the newly arrived forces will mass their heavy artillery and armour and charge the enemy with everything they have while the 2nd wave is already engaged.

Legion Culture & Beliefs
After Vilhem returned to the Emperor’s side and joined his sons the Legion actually begun to make use of more tactical recon teams to strike enemies or plan out assaults days in advance.

Still prepared to die for the purpose of expanding humanities rule and creating a galaxy safe for the people, many Astartes of the Omni Legion display this foresight as they tend to and protect the Imperial Guard as though they were one of their own. This specific outlook is because the legion has embraced that they're weapons created by the Emperor and serve the purpose of war.

Due to the quiet nature of the Omni Legion they'll communicate with one another silently with their vox comms. This isolated lifestyle makes the Astartes hard to approach because of their stern postures but this comes as part of living on battlefields for months to years at a time.

Their fanaticism toward technology has made them close allies to the Adeptus Mechanicus and this shows through their own iconography. Wielding weapons some may consider to be too dangerous or some others have never seen they do it for the preservation of mankind and perfecting the art of warfare.

Legion's Gene-Seed
The physical appearances of members of this Legion are consistently pale with black circles around their eyes, giving them a very dead appearance. This has a consistent 100% chance of occurring.

Many Astartes suffer from a deterioration in their vocal cords that causes them to have a quieter tone that's almost like a whisper and they struggle to speak louder because of their weakened vocal cords their primary method of communicating vocally is with the aid of their helmet's microphone that amplifies their voice. This mutation has an overwhelming 88% chance of occurring.

One additional change is the much thicker bone structure those with the Omni Legion Gene-Seed, this makes the Marines range from roughly 12% to 20% larger than others, it helps seeing as they operate in such hazardous environments and are used to carrying heavy equipment for longer periods of time. This has also made it harder to create Astartes whose bones may tear through their muscles and skin causing them ceaseless pain and agony until they're put down. This mutation has a 35% chance of causing the Astarte's development to fail.

Legion Colours
The armour of the Omni Legion primarily have a silver colour scheme with a red trim along the pauldrons, knees and the plating covering the stabilizing jets of their backpacks. Every Legionnaire has blue eyes on their helmets.

Legion Badge
The Omni Legion's badge is a white coloured Cog Mechanicum icon - the ancient symbol used to represent the Mechanicum and their religious faith, the Cult Mechanicus. This emblem takes the form of a halved human/cyborg skull, which represents the fusion of flesh with the holy machine. This icon is centered upon a white circlet centered on a field of red and surrounded on the left side by a half-cog symbol, which represents the Legion's close ties with the Mechanicum.

Trivia
This article, authored by Cyberslayer128, and transcribed here, for your viewing pleasure, by Algrim Whitefang and Gladius Voss.