Battle of Zakuul

After Eternal Empress Vaylin was killed during the assault on Odessen, the remaining Eternal Empire forces on Odessen surrendered to the Alliance, ending the battle on the ground. However, Vaylin's death also left the Eternal Throne empty, causing the Eternal Fleet's GEMINI captains to go rogue and revert to their most primal function - exterminating all complex life in the galaxy. Eternal Fleet warships left Odessen's orbit and began bombarding heavy populated worlds including Dromund Kaas, Coruscant and the other Core Worlds, and Zakuul itself. The Eternal Fleet had also established a blockade around Zakuul, blasting any ships that attempted to land or leave, protecting the Eternal Throne in a ray shield, while also laying fire to the Spire itself, with entire buildings collapsing and bodies lying in the streets.

The people of Zakuul had not yet received news of the Empress' death, with some speculating that she was the one who ordered the slaughter, while others correctly assumed that Vaylin was dead and the Eternal Fleet had gone mad. Vaylin however was not completely gone, as in the moment of her physical death, Valkorion absorbed her spirit into the Alliance Commander's body which he already occupied, giving the Immortal Emperor the key to conquer his host's mental defenses. Meanwhile, since claiming the Eternal Throne was the only way to stop the destruction, the entire Alliance leadership boarded the Gravestone and departed for Zakuul. The Commander also ordered Lana Beniko to bring with them Dramath's holocron which they recovered on Nathema and which, they hoped, could be used as a weapon against Valkorion.

The Gravestone, protected by the Alliance fleet, dropped out of hyperspace in orbit of Zakuul, which was completely blockaded by Eternal Fleet warships. However, the Gravestone had an advantage in form of upgrades that were installed based on schematics obtained on Iokath and provided a boost to the vessel's shields, allowing them to withstand a concentrated fire from the Eternal Fleet and break the blockade, after which the Gravestone then began firing the omnicannon, destroying multiple warships with each shot. The Alliance Commander prepared to head down to the surface, and former Emperor Arcann and his mother Senya Tirall volunteered to accompany them in an escape pod, which the three of them used to land in the Garden of Izax as fire and destruction reigned around them.

They then made their way towards the Spire, along the way engaging skytroopers and Knights of Zakuul, who did not yet know that the Empress they were serving was dead. At the entrance to Eternal Throne Spire, the Knights blocked their way with a Tyth's Gauntlet, but Indo Zal and Zakuulan rebels unexpectedly showed up to provide support, destroying an Eternal Empire Walker with a rocket launder. Fighting their way through waves of security, the Commander, Senya and Arcann eventually reached the turbolift that led directly to the Eternal Throne. After entering the room for the first time in almost a year, Arcann was taken aback at seeing his old Throne and, feeling the need to atone for his past crimes, offered it to the Commander, proclaiming them a more worthy Emperor than he ever was. The Commander claimed the Throne, which send a shock through their body and send a signal to the Eternal Fleet, which had immediately gone silent all across the galaxy, stopping the bombardments before reaching truly horrific casualties.

However, as soon as the Commander was on the Eternal Throne, Valkorion turned on them and revealed his true goal, forcing the Commander to kneel and proclaiming his desire to eradicate the Commander's mind and take possession of their body, after which he shocked them into nothingness. At this point the Throne room was breached by attacking skytroopers, forcing Senya and Arcann to hold their ground before they could be of help. The Commander awoke inside the abyss of their own psyche, wearing Valkorion's form in a subconscious attempt to save their identity from being completely erased. Traversing the bizarre mindscape, the Commander cleansed their corrupted memories, which revealed the thoughts and motivations Valkorion had while inhabiting their body. Locating a mental representation of the Holocron, the Commander regained their identity, causing Valkorion to manifested in his usual form, intending to finish the work of destroying his vessel's consciousness.

The Commander resisted and Valkorion summoned Vaylin's enslaved spirit, dominating her will and commanding his daughter to destroy the Outlander. The Commander battled Vaylin in the mental mindscape and prevailed, but Valkorion easily restored her spirit, after which the Commander used the representation of the holocron to free Vaylin from her father's mind control. At this point, Arcann has joined them inside the Commander's mind by meditating at the physical holocron still located in the Throne room. The Commander and Arcann convinced Vaylin to join them against Valkorion, and the three of them attacked the Immortal Emperor. After toying with them for a while, Valkorion destroyed the holocron, claiming that nothing was able to stop him. However, since his spirit was now bound to Vaylin's and shared her weakness, the Commander used Vaylin's mental conditioning to turn the tables on Valkorion and rob the Emperor of his own strength. With Valkorion overpowered and weakened, Senya joined her children in the Commander's mind and together the family watched the Immortal Emperor's final words and moments, until the Commander put a final end to his millennia-long existence.

After Valkorion's essence was destroyed, the Commander, Senya and Arcann found themselves back in the Eternal Throne room, where Arcann was able to confirm that he no longer felt his father's presence, who was gone for good. Senya then opened a system-wide holochannel for the new owner of the Eternal Throne, who made an address towards the galaxy and proclaimed an age of the Eternal Alliance. In the following days, the Alliance had established complete control over the Eternal Fleet and what remained of Zakuulan military force, appropriating its vehicles and recruiting the personnel for the armed force of the new Eternal Alliance, which had grown from a small-scale insurrection to become one of the major galactic powers alongside the Galactic Republic and the Sith Empire. For a while, the other governments were busy with recovery efforts on the world that suffered from the Eternal Fleet bombardment, but before long, both were preparing for a renewal of open scale war, put on hold since the Eternal Empire conquest. The Eternal Alliance had relocated the Eternal Throne from the Spire to Odessen, where it was installed in the Alliance base, issuing the Commander's new orders directly to the Eternal Fleet.

Several aspects of "Chapter IX: The Eternal Throne" can play out differently, depending on player's past choices. Either Vette or Torian Cadera are killed by Vaylin on Odessen during "Chapter VIII: End Times" while the player has to choose which one to save; the survivor will show up on the Gravestone before the battle and during the Eternal Alliance celebration at the very end. Likewise, either Aric Jorgan or Kaliyo Djannis can be killed or exiled by player during Knights of the Fallen Empire "Chapter XIII: Profit and Plunder", in which case they will not show up during the battle. If the player previously killed or exiled Koth Vortena, Hylo Visz will take his place as the captain of the Gravestone, piloting the vessel and using the upgraded shields to breach the blockade around Zakuul.

If the player previously killed Arcann and Senya Tirall, Theron Shan and Lana Beniko will accompany them to the Eternal Throne room instead, although the spirits of Arcann and Senya will still show up to help player defeat Valkorion. If during "Chapter VI: The Dragon's Maw" played had ordered Indo Zal to lead Zakuulan rebels into fight instead of taking to safety, Indo will still show up to provide assistance, but will mention that the rebels have lost their faith in the Alliance. If Arcann was killed without achieving redemption, both his and Vaylin's spirits will be absorbed by Valkorion and ordered to attack the player, who will free them with Dramath's holocron and convince them to join their side, despite having killed them both. If during "Chapter VII: Into the Void" player has kept Lord Dramath imprisoned in his holocron, his spirit will show to assist the player, confronting his son, killer and tormentor. After defeating Vaylin's spirit, Dramath will attack Vitiate, piercing his defense as the cost of his life, finally achieving oblivion after centuries spent between life and death.

If previously killed on Voss, Senya will still appear in the player's mind to help finish Valkorion, though her lines and actions will be exactly the same as in the outcome where she remains alive and enters the player's mind via holocron. After Valkorion is defeated, player can address the galaxy as a peacekeeper in a Light Side option or as a new Emperor in a Dark Side option. In the Light Side option, people of Zakuul are left free to rule themselves and the Eternal Fleet is transformed into a peaceful armada delivering refugees and supplies to help the galaxy rebuild after the war. In the Dark Side option, Zakuul explicitly surrenders to the Alliance control, with Valkorion's name expressly being forbidden from being spoken again, while the Eternal Fleet is used as a deterrent to keep the other galactic powers from challenging the Eternal Alliance. This choice affects several lines and cutscenes during subsequent events on Iokath and Umbara.