Gemm is a planet in the Perseus arm of the Golden Branch star sector. It is a Diasporan planet that was previously an industry hub and population center[1] before becoming a devastated radioactive badlands. There are still millions of inhabitants on the planet. It is also the home of the Divine Fortitude.
During the Golden War, an Apostolosian deep space fleet attacked Gemm's capital, killing civilians and destroying the surrounding area. This left millions of refugees on the planet. Some of these refugees were brought to Glimmer during the Kingdom arc.
Over the course of the series, outside political influence would change Gemm's allegiance. The Golden Demarchy attempted to seize the planet away from the Diaspora, and gained support from some of the local population. Ariadne led an underground movement in support of the Demarchy, and they were able to deal a blow to Fortitude.
After the events on September, the planet landed in the hands of the Free States of Kalliope under the leadership of Hudson Thorne. However, Horizon Tactical Solutions and other separatists on the planet split away from Kalliope, becoming part of the Free States of Gemm.[2] After the finale, Gemm grows as a planet, becoming similar in population to Counterweight. It's also able to repair its atmosphere after 20-30 years of work.