Invasion of Voss

During the Battle of Odessen Senya Tirall rescued her critically wounded son Arcann from the debris on his flagship, managing to take the former Eternal Emperor into his personal shuttle and flee into hyperspace in hopes of redeeming him. In Arcann's absence, his sister Vaylin claimed the Eternal Throne and, as the new Empress of Zakuul, declared a bounty on her mother, searching the galaxy for months. At one point Senya came into contact with a dissident group of Zakuul Knights who were willing to help Senya heal the former Emperor on Ord Mantell. However, Vaylin found out about the Knights and after massacring all of them, waited for her mother. When Senya arrived, Vaylin attacked her and the two fought amidst the burning rhydonium, the fight only ending after Vaylin pierced the hyperdrive of a damaged starship with a lightsaber pike, enabling Senya to escape with Arcann. Though she intended to kill her mother, Vaylin took this opportunity to track her back to Arcann, leading her to Voss. Senya made it there to bring Arcann to the Shrine of Healing, where she hoped to use the Voss healing ritual to heal both Arcann's injured body and his spirit, curing him of the hatred that had consumed him. Voss had previously already experienced subjugation from the Eternal Empire when a Star Fortress was placed in orbit of the world.

Having followed her mother's trail, Vaylin launched an attack, determined to hunt her family down. At this time, Alliance operatives Theron Shan and Sana-Rae were already on world to meet with an informant who claimed to know of Arcann's whereabouts. Their rendezvous was interrupted when Eternal Fleet arrived in Voss system, and Shan alerted the Alliance about the attack, allowing the Alliance Commander to scramble the Alliance fleet in response. The Eternal Empire began deploying ground forces to the capital city of Voss-Ka, led by Vaylin's new Horizon Guard and composed of Knights of Zakuul as well as numerous skytroopers. From the Eternal Throne, Vaylin ordered her forces to begin the search and torch the planet behind them, and the Eternal Fleet opened fire on Voss-Ka, causing buildings to collapse and fires to spread throughout the capital. Theron Shan attempted to rally Voss commandos to the defense, but their forces were outmatched, and he led a group to take shelter in the Tower of Prophecy along with Sana-Rae.

Emerging from hyperspace, the Alliance fleet arrived in orbit of Voss and—despite the Gravestone not yet being present—successfully engaged the Eternal Fleet. A stolen Zakuulan shuttle allowed the Commander, Lana Beniko, and Torian Cadera with a group of Mandalorian commandos to slip past the Eternal Fleet blockade and reach the burning city of Voss-Ka. Landing in the Republic District, the Alliance and Mandalorian forces engaged Zakuulan Knights and skytroopers in an attempt to retake the capital. After the Republic District was cleared of enemy forces, Theron Shan contacted the Commander and Lana and asked them to assist the Alien Enclave, while Theron and his warriors stayed behind to hold their position. In the Alien Enclave Market Lana and the Commander attacked a massive PA-717 Planetary Assault Goliath; the droid was protected by XD-M8 Remote Mines, but "Deadeye" Leyta and her strike team provided the remote assistance, allowing the Commander and Lana to prevail.

They then moved towards the northern plateau that housed the Imperial District, but the Eternal Fleet bombardment completely obliterated it. Theron then directed them to a location where Voss Commandos provided access to a service tunnel that led the Commander and Lana to the Voss-Ka Cantina on the other side of the city. Vaylin's forces were gunning after Voss civilians in the Judicial Quarter, but Rokuss and his Gormak soldiers volunteered to save them, leading the Commander and Lana with a clear route to the Tower of Prophecy. Theron met them right outside the entrance and rushed everyone inside, where along with the Voss Commandos the group repelled an attack by sabotage droids, skytroopers, Zakuul Knights, and Horizon Guard.

After meeting with Sana-Rae, the group received a distress call from Senya, who revealed her presence on Voss and pleaded the Alliance for aid, promising that Arcann would join their fight if healed. Though Theron and Lana had different ideas on what do to about Arcann, everyone agreed that it was imperative to reach the Shrine of Healing before Vaylin. The Commander ordered Lana to take the Mandalorian forces and lead them towards the Shrine, while Theron used his shuttle to get the Commander and himself to the Old Paths that lead to the Shrine. To help them break through the enemy forces in their way, Torian delivered the Storm Rider walker to their location, which the Commander and Theron used to stomp the skytroopers in their path.

As they progressed, the Eternal Fleet warships that entered the atmosphere began bombarding the only road to the Shrine, only to Koth Vortena to finally join the fight on the Gravestone and begin using it against the fleet. With the path relatively safe, the Storm Rider had to dispatch an Eternal Empire Walker called the Talon of Izax that guarded the entrance to the Shrine. Theron and the Commander then disembarked and made their way inside past the Voss and Gormak soldiers, who united to defend their homeworld in the face of a larger threat, ending the centuries-long war between two species. Inside the Shrine, the Commander and Theron met with Senya, who was separated from them by a ray shield and bargained for her son's life, promising that once his mind was cured of the hate, Arcann would join the Alliance's cause.

Vaylin then called and addressed the group through a skytrooper holocomm, taunting her family and ordering the Eternal Fleet to bombard the Shrine in an attempt to kill them all, completely destroying the Shrine's upper levels. Senya asked the Commander to hold of Zakuulan forces so that the Voss healing ritual could be completed and rushed to her son after they agreed. Lana and her team of Mandalorians held off Zakuulan forces from pouring into the Shrine, while the Commander and Theron collapsed the tunnel behind them to stop the ones already inside from reaching Senya's position. Senya herself battled and single-handedly defeated a host of Zakuulan Knights, but as it became clear that their position was about to be overwhelmed, Senya ordered the Voss Mystics to take her strength to heal her son.

The Mystics complied and transferred her strength to Arcann, healing his injuries and mending his broken spirit, though this act left Senya comatose. Arcann awoke confused and, witnessing his mother's lifeless body, fled the Shrine back to his shuttle, believing her dead. Having held of Zakuulan forces as long as they could, Lana and the Mandalorians regrouped at Senya's position, where Lana rushed alongside the Commander to intercept Arcann before he could reach his shuttle. However, they were too late to stop Arcann's departure, who managed to get the shuttle in the air despite lacking his cybernetic arm. The Commander ordered Koth to disable the shuttle, but the Gravestone was under heavy fire and unable to assist, leading to Arcann's escape into hyperspace.

At this point, Vaylin had ordered the Eternal Fleet to burn her entire family regardless of casualties on Voss. Just as all seemed lost, the tide of the battle was turned by the arrival of the Imperial Fleet, led by Sith Empress Darth Acina herself. Tired of submitting to the Eternal Empire, Acina joined the Alliance in the open revolt against Zakuul, voiding the Zakuul–Imperial treaty. Harrower-class dreadnoughts opened fire on the Eternal Fleet warships, destroying several of them and prompting the GEMINI captains, granted free will by SCORPIO, to flee in self-preservation.

After her ships had driven the Eternal Fleet from Voss, Empress Acina contacted the Alliance Commander and extended a formal offer of alliance against the Eternal Throne. The Commander agreed to consider Acina's offer and departed directly to Dromund Kaas along with Theron Shan and Lana Beniko. Meanwhile, Vaylin was furious that the GEMINI droids have retreated from battle against her orders and threatened to dismantle them, requiring SCORPIO to encourage the Empress to focus on the big picture. Senya Tirall was transferred to the Alliance base on Odessen, where Doctor Juvard Illip Oggurobb stabilized her condition and began looking for possible treatments for her coma. In the end, although Voss was saved from the full destructive might of the Eternal Throne, it suffered heavy losses, with much of the planet devastated and thousands of Voss and Gormak killed.

Several aspects of the battle play differently depending on the player's choices. Rokuss and his Gormak soldiers rescue civilians only if the player completed the mission to destroy the Voss Star Fortress before starting Knights of the Eternal Throne Chapter I: Wrath and Ruin, otherwise, the optional task falls to the player. Likewise, even though "Deadeye" Leyta makes no actual appearance, her involvement in the battle is mentioned in a special ability available only if the player had previously destroyed the Tatooine Star Fortress. If the player's Dark Side choices caused Koth Vortena to abandon the Alliance and steal the Gravestone, he will participate in the battle independently to protect civilians and will ignore the player's calls for help at every turn.

The biggest difference is caused by the player's choice to either help Senya Tirall in healing Arcann or refuse to assist her. If the player takes the Dark Side option, they will order Lana Beniko and the Mandalorians to attack Senya instead of holding off Zakuulan forces. Senya will hold her own against the Mandalorians before engaging Lana in a duel, which is interrupted by the player's arrival. Arcann escapes without being healed, and blaming Valkorion for her failure, Senya engages the player in combat and is mortally wounded before expiring. Following this choice, Arcann will attack the player to avenge his mother during Chapter VI: The Dragon's Maw and will also be killed, never achieving redemption.