Acina serves as a minor character in Rise of the Hutt Cartel, a major character in Knights of the Eternal Throne, the deuteragonist/primary antagonist of the update DLC War for Iokath, and a major character in Onslaught.
Acina spent her early Sith training in the Sith Academy on Korriban, where as some of her earliest trials as the Sith apprentice she was required to kill local vermin in the tombs located in the Valley of the Dark Lords. She eventually obtained the title of the Dark Lord of the Sith. In 3640 BBY she was chosen by the Emperor's Hand to be the new head of the Sphere of Technology after the death of Darth Karrid at Duro and to watch over a warehouse of powerful technology known as the Arcanum. During that time her position on the Dark Council was strong, as she controlled all access to Arcanum, requiring others Councillors to impress her. However, one of her apprentices had secretly sworn loyalty to the Dread Masters, which allowed their follower Tagriss to organize a Raid on the Arcanum and escape with many dangerous artifacts such as the Darkstaff and the Seeds of Rage. Her position imperiled, Acina was quick to summon help from an Imperial individual to assist in locating and recovering the seeds. Eventually succeeding in recovering the last of the Seeds on Ilum, the Imperial returned them to Acina, who planned to hide them on Ziost.
In 3637 BBY the Eternal Empire of Zakuul revealed itself to the larger galaxy and launched the Eternal Empire conquest on both the Empire and the Republic. Within a year, Dromund Kaas was blockaded and most of the Dark Council members either died or disappeared during the chaos. Darth Acina was the first to recognize that the Sith were outmatched and the only one of the Dark Council to remain by the time Zakuul–Imperial treaty was negotiated by the Minister of Logistics. In a power vacuum, Darth Acina assumed leadership of the Empire and declared herself Empress of the Sith, declaring loyalty to Emperor Arcann who publicly acknowledged her claim.
Acina continued to rule the Sith Empire for the next five years, her rule supported by the majority of the population. As Empress, she bided her time during Arcann's reign, but after his defeat at the hands of the Outlander during the Battle of Odessen, she saw the opportunity to reclaim the Sith Empire's power. Realizing that the Alliance that defeated Arcann would be strong enough to eventually defeat Arcann's notoriously unstable sister Vaylin, she openly defied her heralds, putting an end to an era of Sith submission. When Vaylin's Eternal Fleet launched an Invasion of Voss, Acina set the Imperial fleet to aid the Alliance and its Commander in battle. The timing of the Imperial fleet's arrival proved fortunate, as it was able to drive away the Eternal Fleet and put a decisive end to the battle. In the aftermath, Acina acknowledged the Alliance as an independent power and invited the Alliance Commander to Dromund Kaas to negotiate an agreement.
When the Alliance Commander arrived on Dromund Kaas, Acina sent the current Minister of Logistics Gelmid Lorman to escort her guest from the spaceport. After the Alliance Commander with the advisors Lana Beniko and Theron Shan were brought to Acina's chambers, whothe Empress suggested that she and the Commander should discuss their alliance in private aboard her personal shuttle. In flight and away from prying eyes, Acina assured the Commander that her offer was genuine, and that she had no intention of taking the Eternal Throne for herself. Their conversation was interrupted by a sudden engine failure, requiring Acina to down the shuttle and abandon ship. Now stuck in the wilderness of Dromund Kaas, Empress Acina and the Commander were forced to contend with the planet's dangerous wildlife and lightning storms. The pair eventually discovered that their shuttle had been sabotaged by the GenoHaradan, whom the Empress had always assumed to be a myth. The legendary assassins proved no match for the Alliance Commander and the Empress of the Sith, however, as the pair shortly dealt with the assassins and located their camp. The Commander discovered from the camp's logs that the assassination attempt was organized by none other than Leontyne Saresh, the former Supreme Chancellor of the Republic, in a bid to take over the Alliance.
When they came under heavy fire, Empress Acina and the Commander took shelter in a nearby Sith tomb. As the pair descended further into the tomb's depths, the Empress and the Outlander were confronted by a traitorous Minister Lorman, who was behind the shuttle sabotage, and a GenoHaradan strike team seeking to finish their job. After the GenoHaradan were dispatched, Acina offered the Alliance Commander to decide Lorman's fate. After the Alliance Commander returned to their headquarters on Odessen and dealt with Saresh, Acina contacted the Commander again with a formal offer on an alliance. Shortly afterwards, she pardoned the Imperial officer Malavai Quinn, who had been imprisoned by former Minister Lorman for defiance, and took him on as her advisor.
The Commander's Alliance proceeded to wage war against Vaylin, eventually striking her down. Unfortunately, that left the Eternal Throne empty, leading the GEMINI captains to revert to their basic programming and commanding the Eternal Fleet to bombard inhabited worlds indiscriminately. Acina issued an emergency distress call to the Alliance, who proceeded to claim the Eternal Throne and take control of the Eternal Fleet. Wary of the power the Eternal Alliance now possessed, Empress Acina began preparing her people for war even as cleanup continued on Dromund Kaas from the last Eternal Fleet bombardment.
When the Empire received an anonymous intel regarding an immensely powerful superweapon on a recently rediscovered world of Iokath, Acina sent a detachment of Imperial forces to secure the weapon. While on Iokath, Imperials encountered Republic forces who were after the same objective and were soon joined by the Eternal Alliance's Eternal Fleet. Acina sent Major Quinn as an ambassador to the Alliance Commander, with the orders to sabotage the meeting and escape should the Alliance turned against Empire. The Empress herself made a holocall and formally asked the Commander to side with the Empire against the Republic forces led by Supreme Commander Jace Malcom.
During the events on Iokath, the player has to choose between siding with the Republic of the Empire, neither of which is a Light Side or Dark Side option. The fates of both Acina and Malcom are affected greatly by this decision, with them mirroring each other's role as either an ally to the Eternal Alliance or a person who seeks to activate the superweapon. If the player sides with Republic on Iokath, Acina assumes the Iokathi throne which kills her If the player sides with the Empire, the Republic launches a counter-offensive against the Imperial base on Iokath. Acina meets with the Commander after the initial attack was repelled and the two agree to reclaim weapons from an Iokath weapons cache to gain an advantage over the Republic. As Supreme Commander Malcom threatens to activate a superweapon capable of wiping out all life on Iokath, Acina provides the Commander with a walker called Crimson Talon to storm the Republic base and stop Malcom. Though the Commander and Theron Shan arrive in time and try to talk him out of it, Malcom still activates the superweapon, awakening the Six Gods, which costs him his life. Though leaderless, Republic forces keep resisting and Acina assures the Commander that their future partnership will remain strong.
If the player sides with the Republic, it is Acina who launches an attack against both the Republic and the Alliance and later discovers a backdoor into the superweapon, seeking to activate it without realizing its danger. In this version of the events, Acina taunts the Commander about the superweapon and assumes an Iokath throne, which rejects her input and kills her. Lying wounded, Acina apologizes to the Commander for her mistake, claiming that nothing can stop the awakened Six Gods, before she dies. Since both Imperial and Republic players can side against their original faction on Iokath, neither version of events has any precedence over the other in-game. A newscast overheard during the "Traitor Among the Chiss" flashpoint reveals that she was succeeded by Emperor Vowrawn if killed on Iokath.