Gath Rimmon was a rocky planet covered in highly acidic oceans that suffered from acidic floods caused by the nearly constant storms, which could last for entire Terran years. Gath Rimmon seemed to be semi-aware and is able to create obsidian-skinned xenos creatures, made from its rocky surface, that kills anyone who trespasses on the planet.
The Ayex Commoragh was hidden on Gath Rimmon by the Adeptus Mechanicus Tech-priest and Logis Alsmo Charis. An Aeldari Warlock by the name of Valiel and a squad of Striking Scorpions hunted Charis to this world, but were destroyed by the Heart. In his last moments, Valiel left a psychic beacon on the roof of the cavern where the Heart was locked away.
Years later, a squad of Space Wolves, led by the visions of the Rune Priest Kolja Ravenblade, were drawn to the world where they met Charis, who was also seeking to recover the artefact. Sensing his betrayal, the Space Wolves attacked just as Alsmo, turned the weapon against them. Ravenblade and Baldr Svelok, a Wolf Guard, managed to destroy the Heart by flooding the chamber with acid at the end of one of the planet's flood cycles.
Ravenblade died shortly after as a result of his injuries, leaving the now one-armed Svelok as the only survivor. The rest of the squad had been killed by the Heart shortly after Charis regained control of it. Svelok fled the planet just as the massive floods of the acidic oceans reclaimed much of its surface.
- Victories of the Space Marines (Anthology) edited by Christian Dunn, "Runes" by Chris Wraight