The Marrow Kingdom was an underground civilization in Mercy that arose from the survivors of a catastrophic divine magic incident over a century ago, when its king attempted to resurrect the royal heir. This event devastated much of Mercy's surface, leading the survivors to establish an anti-magic society underground. When Esperanto began colonizing Mercy decades ago, the Coven discovered the isolated kingdom through Marcerine's father and transformed it into a social experiment.
After a failed resurrection devastated the surface of Mercy, the survivors retreated underground and established a strictly anti-magic society. This isolation continued naturally for nearly a century until Esperanto's colonization efforts reached Mercy.
When the Coven discovered the kingdom through Marcerine's father, they recognized an opportunity and began monitoring the isolated society. They installed agents like Spymaster Domia to maintain and study the kingdom's anti-magic culture, exploiting its existing isolation rather than creating it.
The kingdom's isolation ended when a massive orb emerged from beneath Mercy's clouds, exposing its location. Initially overtaken by swamp pirates, the kingdom was eventually reintegrated into Esperanto's administration of Mercy, ending the Coven's decades-long experiment.
The kingdom maintained strict control over its population through an oppressive anti-magic stance, enforced by figures like Akun the Breaker, who became notorious for her relentless pursuit of the Sock Pirates after their escape. Noble families like Tsavo's held significant influence, while magic users like Ping Wing faced persecution.