The pursuit of Lieutenant Sol Rivas, who was accused of "treason" against the First Order, was led by Captain Phasma, along with TN-3465, a First Order TIE fighter pilot, and the BB unit BB-K8. The real reason for Phasma's pursuit was to get rid of Rivas, as he was the only one who knew that she had betrayed the First Order to save herself by taking down the shields of Starkiller Base.
After the Battle of Starkiller Base, Sol Rivas ran away to the unexplored planet Luprora, where he was captured by the R'ora, a scary alien species that lived there. Captain Phasma, TN-3465, and BB-K8 followed Rivas in a TIE/sf space superiority fighter. Over the next four days, Phasma got the humanoid Lupr'or to help her attack the R'ora stronghold. Phasma and her Lupr'or army used generators they found from an old Lupr'or starship to electrocute the Tsw'ells in the lake that protected the R'ora stronghold.
While the Lupr'or were fighting the R'ora, Phasma killed Rivas after they had an argument. Before leaving Luprora, Phasma destroyed BB-K8 and killed TN-3465 to make sure no one knew about her part in the destruction of Starkiller Base. Phasma then made up a story saying that she had killed Rivas for his supposed treason and that her comrades had died in the process.
During the Battle of Starkiller Base, Han Solo, Finn, and Chewbacca forced Captain Phasma, a high-ranking First Order officer, to lower the deflector shields that were protecting Starkiller Base. This left the superweapon open to attack from a Resistance strike force. After being thrown into a garbage compactor, Phasma managed to survive. She used an anti-armor acid to break out of the compactor and went back to the console to erase any evidence of her wrongdoing. However, she found out that Lieutenant Sol Rivas, another First Order officer, had already accessed the defense shield files. To hide her actions, Phasma decided to blame Rivas for her crime.
As Starkiller Base started to collapse because of the planet's damaged fuel cells, Phasma chased Rivas through the base and across the planet's surface, almost falling into magma. Lieutenant Rivas managed to escape to a backup hangar on the surface, where he stole a TIE/fo space superiority fighter. When Phasma arrived at the hangar, she found TN-3465, a TIE fighter pilot, and BB-K8, a BB unit. BB-K8 was fixing TN-3465's TIE/sf space superiority fighter, which wasn't ready for combat. Captain Phasma enlisted TN-3465 and BB-K8 to help her track down Rivas for his supposed treason. The three of them escaped Starkiller Base on the TIE/sf fighter before the planet was destroyed by the stellar energy it had absorbed from a nearby star.
While chasing Rivas through space, Captain Phasma realized that the TIE/sf fighter's weapons weren't working because BB-K8 hadn't finished fixing them. Since she couldn't shoot Rivas in space, Phasma told TN-3465 to follow Rivas. When Rivas' TIE/fo fighter ran out of fuel, he landed on Luprora, a faraway planet in the Unknown Regions that was full of mountains and ocean. Soon after landing, Rivas was captured by the R'ora, an alien species that lived in the water on the planet.
Phasma and her team landed their TIE/sf fighter nearby. After looking at the site where Rivas' fighter had landed, Phasma figured out that he had been captured by some creatures. Phasma then found a settlement across a lake. After changing into regular clothes, Phasma, TN-3465, and BB-K8 waded across the lake to get to the settlement. However, Phasma was attacked by a giant monster with tentacles called the Tsw'ell, but she managed to kill it with her long knife. The humanoid Lupr'or settlers who lived in the village were impressed by her bravery.
Phasma and her team met Jair'i, the leader of the Lupr'or people on Luprora. He told them that his people were descendants of migrants from other planets who had given up technology to focus on fishing and farming. However, rising sea levels and the threat from the Tsw'ells and R'ora had forced them to move to their current settlement. Jair'i told Phasma and TN-3465 that their "friend" had been captured by the R'ora. Jair'i sent a female guide named Dar'en to show Phasma and TN-3465 the R'ora stronghold in an attempt to convince Phasma that it was pointless to try to rescue Rivas.
While examining the R'ora stronghold, Captain Phasma noticed that the water in the lake wasn't as salty as she expected. Dar'en then suggested that her guests leave because of the Tsw'ell monsters that lived in the lake. Phasma later learned that the Tsw'ells slept in the early morning hours, but not for very long. Since she couldn't blast the R'ora stronghold or the Tsw'ells, Phasma became interested in a necklace worn by a young Lupr'or girl.
The young girl led Phasma, TN-3465, and Dar'en to her great-grandmother Ali'ane, who told Phasma that her people still had technology on a ship in the mountains. With the help of Ali'ane's great-granddaughter, Phasma and the others found the ship on top of a mountain. When they returned to the village, TN-3465 tried to get Da'ren to bring everyone in the village, but she only brought the men because of a translation mistake by BB-K8. Captain Phasma managed to impress the Lupr'or by putting on her armor.
Captain Phasma managed to persuade the Lupr'or to help her attack the R'ora stronghold by claiming that she had been sent to lead them to victory. In reality, Phasma planned to use the Lupr'or as cannon fodder while she carried out her real mission to eliminate Rivas for his alleged treason. Using the generators they had salvaged, the Lupr'or electrocuted the Tsw'ells that were lurking in the lake, killing them. This allowed Phasma, TN-3465, and the Lupr'or to row their boats across the lake and climb the walls of the R'ora stronghold.
Under the cover of rain, Phasma and the Lupr'or descended down the battlements and attacked the R'ora in a fierce battle. While the R'ora were distracted, Phasma and TN-3465 approached the R'ora tower in the center of the stronghold. Captain Phasma ordered TN-3465 to watch their exit while she went into the tower to deal with Rivas. Inside, she found Rivas, who was battered and tied up. Phasma tried to force Rivas to admit to his alleged treason, but he instead confronted her about her role in the destruction of Starkiller Base. To hide her wrongdoing and shameful secret, Phasma killed Rivas with her blaster.
Unbeknownst to Phasma, TN-3465 witnessed her actions and tried to hide her knowledge of Phasma's role in the destruction of Starkiller Base by expressing concern for the Lupr'or. Having eliminated the so-called "traitor", Phasma showed indifference to the Lupr'or, claiming that they were colonists trying to take Luprora from the native population. Justifying that the Lupr'or were not suitable for the planet's evolution, she abandoned them to the rising tide.
Before leaving Luprora on the TIE/sf fighter, Captain Phasma disintegrated BB-48 with her blaster before forcing TN-3465 to raise her hands at gunpoint. TN-3465 pleaded for her life, but Phasma reiterated that she was a survivor who was determined to eliminate all loose ends. Phasma gave TN-3465 a quick death by shooting her through the chest. After laying her former comrade and BB-48 to rest, Phasma departed on the TIE/sf fighter.
After getting rid of Sol Rivas and the potential witnesses, Captain Phasma filed a false report blaming Lieutenant Rivas for lowering Starkiller Base's shield. She claimed that she had been unable to bring Rivas back to the First Order alive for justice, but had executed him for his crimes. Phasma also claimed that TN-3465 and BB-K8 had died during the mission.
After returning to the Resurgent-class Battlecruiser Finalizer, Captain Phasma reported to her commander General Armitage Hux, who asked her about her absence. Phasma told General Hux about her mission to hunt down Rivas for his alleged role in the destruction of Starkiller Base. Satisfied with her account, Hux allowed her to return to her divisional duties and praised her for her purported devotion to the First Order; unaware about the true events that had led to Starkiller Base's destruction.
The hunt for Rivas is the main plot of Star Wars: Captain Phasma, a four-issue comic book from 2017 published by Marvel Comics as part of the Journey to Star Wars: The Last Jedi promotional campaign. This comic explores what happened to Phasma after the events of Star Wars: Episode VII The Force Awakens. The events of the mission were created by Kelly Thompson, illustrated by Marco Checchetto, and colored by Andres Mossa.