As head of the Dark Council's Sphere of Technology, Darth Acina initially appeared uninterested in the political machinations of her peers. However, when Darth Marr's death at the hands of the Eternal Empire incited panic and infighting among the surviving council members, Acina was the first to understand the Sith were overmatched.
She declared loyalty to Arcann and--allegedly--helped him eliminate several council members who refused to bow before the Eternal Throne. With her rivals out of the picture, Acina declared herself Empress of the Sith, and Arcann publicly acknowledged her claim. Whispered gossip suggested their relationship went much deeper than mere political alliance, though little exists to substantiate those rumors.
Some accused Acina of cowardice, but the cunning Sith was merely biding her time. With Arcann's fall and the growing strength of the Outlander's Alliance, Acina saw a chance to strike back at her conquerors, and her open defiance of Empress Vaylin heralds an end to the era of Sith submission.