Bunker

In one universe, underground bunkers were one of the two types of habitats built by the human colonists of one planet, alongside the floating Citydromes. Bunkers functioned as secure, self-sustaining communities, growing their own food using Synth-Fields.

Billy and Trent's mother and father maintained a bunker. After they retired, responsibility its running transferred to their eldest and favourite son Trent. A jealous Billy ended up arranging for a group of Kievs to attack the bunker, killing all its residents — including Billy and Trent's parents — except for the brothers themselves. (COMIC: Betrayal of Brothers)