Cerulean is the homeworld of the Order of the Blue Thorns. Consisting vastly of deep blue oceans with their tides crashing against isolated islands, Cerulean was uninhabited before the Prophet Zeresh led her fledging Order there, selecting Cerulean for the hue of its seas and oceans. The people of Cerulean live spartan lives, scratching out lives on the craggy rocks and hunting the descendants of invasive species that they brought with them. Life is a struggle, but they are happy for this struggle: they see this as their representative of the Emperor's and Guilliman's struggle to help humanity survive in the galaxy, and for their efforts, they do not go hungry. At the peaks of these island communities sit the long-dormant landing craft that ferried the populations of each island to their current communities. They have since been cannibalised, stripped down, and now their cavernous holds are vast shrines to the Emperor, maintained by a single squad of Sisters of the Blue Thorns. Each ship-church is a barracks, armoury, place of worship, and civic centre for the squad and the settlers who share the island. The Sisters often act as arbitrators of law and justice on each island, ruling from their ship-church. However, they are most often found in deep meditation, as the Prophet Zeresh was, or in training drills. For when the Order of the Blue Thorns marches to war, they unite from all the dotted island communities across the planet into one seamless fighting force.