The Sea Lions started as an off-shoot from the Katagian invasion force sent to conquer Ren Shaar during the famine of 1191 PD.
By then, the previous Chosen King was already unpopular. The Katagians vied for grassroots allegiances by offering starving locals food, supplies, and protection from brigands. This was their ultimate strategy for winning over the Ren Shaari people.
It worked, and it didn't. In the rural countryside, the starving populations sided with the Katagians. But those who besieged and then held the streets of Ren Shaar were not as welcome. Common history knows what happened there next: a three-day new year's festival devolved into "The Bloody Revel"—a storming of the Katagians' base of operations by disgruntled civilians who then managed to slay their leading admiral.
Those who survived the revolt fled into the countryside, potentially regrouping. Nowadays, that group—calling themselves the Sea Lions—are a decade removed from the wanton political ambitions of Katagia; they are no longer invading soldiers but respected residents of local villages and communes that have been rebuilt since the famine's worst days. Moreover, they are populists seeming to desire home-rule; after all, none of them had a say in King Hadar's election and a decade of politics since.
It is currently unclear whether the Sea Lions and their supporters intend to usurp Hadar's authority or separate from it. It is also unclear who leads the organization and how powerful they truly are, or whether they have agents within the city walls. Regardless of their secrecy, the Court of The Chosen now considers them the most serious threat to peace and status quo in Ren Shaar.