Marius Gage - The Debt of Vengeance: Since his takeover of the Legion in the fourth decade of the Great Crusade, Roboute Guilliman had succeeded in transforming the XIIIth into an intricate and highly functioning weapon of war, and in doing so had built upon a track records of success in battle which held very few stains of defeat. For more than a half a century the Legion had gone from strength to strength, waging Compliance actions and liberating worlds for the Imperium across the eastern reaches of the galaxy, and forging the realm of Ultramar in the process. Yet for all this, Roboute Guilliman knew that a shadow of doubt afflicted his Legion's soul. That doubt had its origins in its darkly storied defeat in the Osiris Cluster Rebllion a few short years before the Primarch's reuniting with his Legion. Marius Gage's tenure in command had commenced with this disaster, and it became a baleful influence in the psyche of the Legion, a thing which while left unspoken nevertheless had power, and that even seemed to cast a pall over the Legion's recruits unborn when the battle was lost. The Primarch knew that the only way to purge his Legion of this shadow of the mind was to find once more the xenos known as the Osirian Psybrids, and with the Ultramarines at his back, destroy them utterly. To this end, ever since he had first reviewed reports of the action when he took over his Legion, Roboute Guilliman had begun planning the Psybrids' destruction.In the decades as his Legion had gone from Compliance to Compliance, war zone to war zone, the Primarch had never stopped running continued theoretical battle scenarios against the macabre and powerful xenos, knowing that one day they would make their reappearance and that he and his Legion would be waiting. But decades passed and they did not return. Only at Maxilla Veritas near the Maelstrom, twenty-six standard years after the Osiris Rebellion, was the evidence for the Psybrids' involvement considered viable. But by the time fast cruisers from the Ultramarines fleet arrived, the trail was already long cold and the planet's dead bore silent witness to the Psybrids' passing. It was in the closing segments of 899.M30 that conclusive word finally reached the Ultramarines Primarch that the Psybrids had not only been encountered, but met in battle. The Primarch's plan of attack was a shockingly direct one. His fleet didn't pause for a long range bombardment or present a broadside and pound the enemy at close quarters, instead, he ordered his Legion to conduct a full boarding strike without prelude. Guilliman drove the core of his fleet and with it nearly 100,000 Ultramarines into the heart of the enemy.One by one the towering hourglass vessels of the Osiran Psybrids fell, either torn apart by explosive charges from within, or rent to flinders in the crossfire of the waiting Ultramarines' echelons as they tried to break free. There was no escape. As the Psybrids died, so too did their Ork slave armies still warring on the ground. The blood price of the battle had been high enough, several thousand Legionary casualties, and many among them veterans of his Legion's Terran roots, eager to be the first in battle in order to expunge the failing of the past. But it had been a price willingly paid for vengeance, and it would be a price and more that the Ultramarines Legion would willingly pay again in the future.