Vincent, Yuffie, Reeve and Shelke manage to escape from the complex just in time for Cid to arrive with the Shera. With help from Cloud and co., the remnants of the WRO plan to lauch a simultaneous land-air attack on the remains of Midgar and the home of Deepground. What they don't know is that the Tsviets are waiting for them with an army of their own. On the Shera, Shelke struggles to deal with her sister's sacrifice and her abandonment by Deepground, and Vincent is seen to be gradually losing control over Chaos (though Lucrecia appears to help him regain composure). Eventually, Shelke decides to help Vincent and the WRO, though she insists that it is in her own best interests: while in Deepground, her main mission was to collect the fragments of Lucrecia's research on Omega and Chaos from the worldwide computer network and arrange them in her own mind to help find the Protomateria. However, this had an unintended side-effect: Lucrecia's thoughts and emotions began to mix with her own. On the WRO's side, as well as providing them with detailed information on Deepground, she can use the data collected by Vincent to complete the collection, remove it from her mind, and regain control of herself.
Using an SND, Shelke explains Lucrecia's findings on Omega WEAPON and Chaos:
Soul wrought of terra corrupt
Quelling impurity, purging the stream
To beckon forth an ultimate fate
Behold mighty Chaos, Omega's squire to the lofty heavens.
Omega WEAPON activates when Gaia senses that it is in fatal peril, gathers the entirety of the Lifestream using itself as the container, and ascends into space to find a new planet on which to deposit it and begin life anew. Without the Lifestream, the remains of Gaia would wither and die, crumbling into dust. As found by Cait Sith earlier, Deepground have been collecting people with pure Lifestream currents (i.e. not infected with Geostigma) to slaughter them en masse and dupe Gaia into activating Omega WEAPON early. The appearance of Chaos heralds that of Omega.