Cut off from the main Tyranid fleet, the Tyranids in Sub-Sector Aurelia are a scattered and disorganized nuisance at the start of their campaign in Dawn of War II: Retribution. When organized by the Hive Mind they are a lethal force that strikes system after system, stripping all life from planets in their path. The Hive Lord leads the swarm in their campaign to rebuild the psychic link with the main Tyranid fleet and finally consume Sub-Sector Aurelia in its entirety.
The opening scene of the Tyranid campaign features the Hive Lord beginning to rebuild the psychic link with the main Tyranid fleet, using splintered remnants of Hive Fleet Leviathan that were cut off during the Tyranid invasion of Sub-Sector Aurelia.
Like many of the other races campaigns in Retribution the Tyranid campaign features the same missions in the same order. However, it appears that much of the dialogue and story structure in the missions was designed for the space marines or the imperial guard and appear to have little relevance to the motivation of the Tyranids whose intention is simply to reassemble the swarm and then consume the subsector.
If the Tyranids are victorious, the final cutscene shows an imperial log filed 43.6 years earlier revealing the fate of the Aurelia subsector.
Having quashed the threat posed by Kyras, the newly assembled splinter fleet unleashed the full might of the Tyranids upon subsector Aurelia. The Exterminatus fleet was driven away, and whilst the local planetary garrisons attempted to prevent the advance of the swarm, the infighting and planetary conflicts had already crippled and divided the Imperial forces.
Ultimately, 94% of all guardsmen stationed in the sector are wiped out before they finally withdraw. The fate of the various Chaos forces, Ork hordes, Eldar strike forces as well as the traitor Blood Ravens and Guardsmen remains unknown, but given that they had limited ways escape it is likely that their faction's were decimated or completely wiped out by the swarm.
As for the loyal Blood Raven companies, - the loyalists refused to abandon their recruitment worlds and despite a valiant last stand were completely destroyed!
The final shot, shows the Tyranid army, comprised of many different bioforms assembled en masse. At the head of it all is the Swarmlord, who unleashes a bestial roar signifying the Tyrannic victory, as it prepares to lead the new assembled splinter fleet on the path of further conquest and extermination!