Nadir-IX was once a failed corporate terraforming project: a world where introduced fungi and algae ran out of control, blanketing continents in choking mats of biomass. The air clogged filters. Engines fouled. Entire research domes were swallowed over the course of a single storm season.

The first Verdant gene-clans were dropped here as a desperate experiment, modified settlers designed to withstand biohazard overload. They not only survived, they learned to read the cycles of overgrowth and collapse, to seed corrective species, to walk the treacherous mats as others walk city streets.

Today, vast "mat-cities" ride the surface of Nadir-IX like slow, living ships, anchored to particularly stable nexuses of fungal growth. Generations of Covenant have grown up listening to the soft thunder of spores against the hull.