"I wear the red of the blood staining the hands of the xenos heretics. I wear the red of the grieving rage that enraptures the followers of the fallen Angel, united in delivering righteous vengeance upon the enemies of the God-Emperor. I wear the red of the dawn on every blood-soaked planet we will bring our crusades to! I wear the red of the Aetherian Warriors!"
―A battle prayer of the chapter.
The Aetherian Warriors are a Twenty Fourth Founding Successor Chapter to the Blood Angels. Being descendants of such a vicious chapter grants them the same skills of their Progenitors, unfortunately this also means they suffer from the Black Rage and the Red Thirst as well. It was a surprise when, for several decades, none of the chapter's members suffered from the geneseed's common afflictions. However, when it did occur, it was much more severe than the other successor chapters, often breaking out in horrible spurts.
Their creation came about due to a large increase in Chaos raids and Ork attacks along the fringes of Imperial space along the border of Segmentum Obscurus and Ultima Segmentum. This has lead to the chapter having a specialization to combat these enemies. Although they were created to fight Chaos, heretics in particular, and Orks, the Aetherian Warriors have seen deployment all across Imperial space to combat all threats to Mankind.
While being a mostly Codex-compliant chapter, they focus heavily on Assault Marines and dropping in the midst of enemy formations. Their Assault Marines are famed for their viciousness which other Blood Angels successors might mistake as the Marines falling victim to the Black Rage or Red Thirst. While this is incorrect, when an Assault Marine gripped in The Flaw, their ferocity is magnified tenfold, carving their way through hordes of enemies.
In M40, in response to an increase in Chaos and Ork attacks, and a lack of Space Marine chapters based in or near the Cordoine Sector, it was decided during the twenty fourth founding that a new chapter would be needed to defend Imperial space along the area of space between Segmentum Obscurus and Ultima Segmentum. Due to the ferocity of the hostiles, and the frequency of their attacks in the region, it was decided that the chapter would need the geneseed of an equally vicious chapter, and thus the Blood Angels' geneseed was chosen.
Veteran Sergeant Terzo Pesaresi of the Blood Angel's 1st Company was chosen to lead the new chapter as it's first Chapter Master, where he and his new command staff began the long process of recruiting the chapter's first marines. The process was long and arduous, with the constant fear of the Red Thirst and Black Rage on the minds of Pesaresi and his staff, eventually by 723.M39, the chapter was at full strength and ready to undertake its first crusade for the Emperor, after which, the Cordoine Sector was renamed the Aetherian Sector.
That first test of the new chapter would be the Aspilia Crusade, which was undertaken in 725.M39, to purge the Aspilia sub-sector of an indigenous xenos species that had been holding up Imperial shipments and fleet movements for several months. The Aetherian Warriors arrived to attack the outer most inhabited system, Seaotania, a very large ship manufacturing plant located at it's capital, Seaotania V. The fall of Seaotania V would cripple the xenos' ship production and relieve beleaguered Imperial naval forces.
The Second and Third companies were deployed via drop pods to the surface of Seaotania V, fifty kilometers from the city's capital, by the Strike Cruisers Glorious Obscurity and Potent Wisdom. They were to assist the 483rd Cadian Shock Troopers and the Arcadian 347th Armored Regiment, whom were both pinned down by heavy xenos plasma artillery. As they made planetfall, they soon discovered that both regiments had been decimated, both by enemy artillery and armored attacks.
With both regiments at quarter strength, taking out not only the artillery emplacements, but the capital itself would be considerably more difficult. Nonetheless they moved onwards, determined to prove themselves worthy to fight in the Emperor's name. Trekking on through the sludge surrounding the capital and shipyard, elements of the 3rd Company were separated and surrounded by heavy xenos tanks, which with heavy plasma cannons and thick armor killed many marines until they were eventually stopped by a young Devastator Marine brought along from the Blood Angels during the Chapter's founding, named Cristoforo Siena, future Captain of the 2nd Company. With his Sergeant dead, Siena was the most experienced marine there and quickly took charge of the situation, leading the remnants of the group and Guardsmen to where the rest of 3rd Company had arrived outside of the capital city.
Once inside the city walls, brutal urban fighting commenced, with the Assault Marines present showing off the ferocity that the chapter would later be known for. Carving their way through the legions of foul xenos, they paved the way for the entirety of 2nd Company and several Guardsmen regiments to enter the city, butchering the aliens inside. Within the week, the capital city had fallen, signalling the effective capture of both the planet and the system, with the shipyards being commandeered by the Adeptus Mechanicus.