A struggle among the primarchs of the Breen Imperium for a vacant throne in 3191, which became entangled with the search for the Progenitors' technology through the fugitive Breen prince L'ak.
The Breen succession crisis forms part of the last season of Discovery. In Mirrors the courier L'ak is revealed to be Breen, the nephew of Primarch Ruhn, who put a price on him after he fled with Moll. In Erigah the Federation learns that six primarchs are fighting over the empty throne and that L'ak, as a direct heir known as the Scion, could settle the matter for whoever holds him.
L'ak is wounded and dies in Federation custody after an overdose taken during an escape attempt. Ruhn takes the body, and Moll goes with it in the hope that the Progenitors' power can bring him back. In Labyrinths Ruhn attacks the Eternal Gallery and Archive, and Moll kills him and takes over his dreadnought with the backing of his soldiers.
In the finale, Life, Itself, a rival primarch, Tahal, heads for the scene, and Saru turns her fleet back with a bluff. The question of the throne is left open.