Warning! Spoilers ahead for Halo episode 2.
Halo episode 2 introduces The Rubble, a safe haven in the galaxy where those seeking refuge can live a free life, far from the eyes of the Covenant and the UNSC. Home of Soren-066, the only SPARTAN-II dropout and John-117's friend, Master Chief takes Kwan Ha to The Rubble in an attempt to evade the UNSC forces after he went rogue, refusing to kill Kwan while also keeping the Forerunner artifact in his possession. The Rubble is also a location that's been referenced in the tie-books and comics, having its own history in the games' timeline that the new live-action series clearly takes inspiration from.
In Halo episode 1, Master Chief and his SPARTAN unit Silver Team were tasked with intercepting a Covenant attack on the colony world of Madrigal. This is where John-117 came into contact with Kwan as well as the Forerunner artifact the Covenant warriors had been searching for. Touching the artifact, Master Chief ended up activating the device which gave him visions—potentially his own fragmented memories that Doctor Halsey and the SPARTAN program had removed during his training. This is what motivates Master Chief to defy orders, sparing Kwan's life and heading for The Rubble as a means to escape the UNSC, giving him time to learn more about his connection to the artifact (revealed to be a Forerunner keystone).
Related: How Cortana Is Created In Halo: Origin & Flash Cloning Explained
Making its first appearance in Halo: The Cole Protocol by Tobias S. Buckell, The Rubble is one of the few hidden areas in the galaxy that wasn't under the control of the UNSC or the Covenant. That being said, the version seen in the new Halo series doesn't seem to be as complex as the one from the
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