Demetrian Titus - Deathwatch Service: After a standard century of captivity by the Inquisition, Inquisitor Thrax led an operation against the traitorous Grey Slayers Chapter, who had become corrupted by the insidious machinations of the Dark Gods. Leading a large retinue of Grey Knights upon the corrupted Chapter's homeworld, they began to purge the Heretic Astartes in earnest.However, during the conflict, Thrax was possessed by a Daemon, and in turn, was killed by his retinue of Grey Knights. In the wake of Thrax's death, forces drawn from the Red Hunters Chapter were dispatched to investigate and secure the Inquisitor's holdings. In a remote Inquisitorial watch station far to the galactic south, a Red Hunters kill-team discovered almost a score of Space Marine interrogation subjects locked in stasis cells, preserved from the passage of time. Titus' story could have come to an end there, had the Inquisitor responsible for overseeing the seizure of Thrax's materials felt inclined to conceal the shame of her fellow Inquisitor. Instead, Titus, and several other warriors of various Chapters who had attracted Thrax's attention, were conveyed to the Deathwatch watch fortress of Watcher Keep to be evaluated.After being found free of Chaos taint or disloyalty, Titus would eventually enter the service of Watcher Keep as a Deathwatch Black Shield, his former identity unknown to those he fought alongside. Having received no word from his brethren since his incarceration, he came to believe he had somehow brought shame upon his name and that of his beloved Ultramarines and determined that he was not worthy to bear the Chapter's name. Overcome with shock and grief at his discommendation, Titus had all of his former Chapter's heraldry purged from his battle-plate and assumed a self-imposed exile as an outcast Black Shield.If he could serve the Imperium and his Emperor as an alien-hunting battle-brother of the Deathwatch until death claimed him, he would do so gladly, having no more desire for personal glory than he did at the start of his life as a Space Marine. Assuming the name "Nullus," Titus honourably served alongside his fellow battle-brothers in the Deathwatch for many standard years. During this point in time, unbeknownst to Titus, the Ultramarines' primarch Roboute Guilliman had been resurrected on Macragge during the Ultramar Campaign of the 13th Black Crusade, and now once again served as lord commander of the Imperium and Imperial Regent.Guilliman led his newly declared Indomitus Crusade against the various enemies of Humanity, as the galaxy had literally been split in two by the opening of the Great Rift at the start of the Era Indomitus, a galaxy-spanning Warp rift formed in the wake of the destruction of the Fortress World of Cadia at the hands of the Warmaster of Chaos, Abaddon the Despoiler. However, this crusade left many worlds weakened after committing large numbers of troops to the war effort, leaving them more vulnerable to invasion.During this time, the Fourth Tyrannic War began in the Segmentum Pacificus, as swarms of Tyranids, ravenous extragalactic aliens that threatened to consume all life in the Milky Way, invaded the already-beleaguered strongholds of Humanity in the galactic west.