A Mandalorian warrior and artist who lived during the Age of the Empire, Ketsu Onyo studied with her friend Sabine Wren at the Imperial Academy on Mandalore. At some point, they decided to escape the Academy, Ketsu helped her friend escape from the academy and the two became bounty hunters. However, Wren alleged that Ketsu became "greedy" and left her for dead while she alone joined Black Sun. Meanwhile, Sabine survived and joined a group of rebels that operated from the starship Ghost and was part of a larger rebellion against the Galactic Empire.
Several years later, Ketsu crossed paths with her former friend Sabine on the planet Garel. Onyo had been sent by Black Sun to collect the GNK-series power droid EG-86, who was carrying information of vital importance to the rebellion. The droid was scheduled to arrive on a GX1 short hauler at Garel City's spaceport. However, Ketsu's mission was complicated when she discovered that Sabine and two rebel associates, the astromech droid C1-10P and the human Jedi Padawan Ezra Bridger, had already picked up the courier droid. Shortly after, Ketsu emerged from hiding and confronted Sabine.
After a tense reunion, Ketsu demanded that Sabine and her friends surrender EG-86. She also told Sabine that she would have been better off dead rather than joining the rebellion since the Empire had put a bounty on Sabine's head. Wren refused to back down and the two former friends prepared for a showdown. However, their confrontation was interrupted by the arrival of a stormtrooper patrol. When the stormtroopers demanded that they leave the spaceport, Onyo opened fire on the stormtroopers with her blaster; sparking a three-way gun battle. In the midst of the fighting, Sabine and her rebel associates managed to escape with EG-86 on a stolen shuttle. However, one of the rebels, Ezra, was separated from his comrades after falling out of the side door.
Ketsu was then surrounded by stormtrooper reinforcements who held her at gunpoint. However, she turned the tables on them and took the stormtroopers out in hand-to-hand combat. She then pursued the rebels on her personal starship Shadow Caster. In space, Ketsu quickly caught up with the rebels' shuttle and managed to disable its hyperdrive. Ketsu then shot open the shuttle's side door, causing a hull breach which sucked Chopper out into the vacuum of space. Satisfied that she made her point, Onyo brought the Shadow Caster face-to-face with the rebels' shuttle and repeated her ultimatum to Sabine.
Unknown to Ketsu, Chopper had survived the breach and had managed to use his rocket boosters to sneak up on the Shadow Caster. Having noticed that Chopper was sabotaging the Shadow Caster's main turbolaser turret, Sabine deliberately prolonged their conversation to give Chopper enough time to complete his work. When Onyo expressed pride at working for Black Sun, Sabine derided the crime syndicate as a bunch of slavers and assassins. After Sabine rejected her ultimatum again, Onyo reluctantly opened fire on Wren's shuttle only to discover that her turret had been sabotaged. This gave enough time for Sabine to escape in her shuttle.
However, Onyo managed to trap Chopper with the Shadow Caster's tractor beams and took him prisoner. Communicating with Sabine over the intercom, Sabine offered to trade Chopper for EG-86. Unwilling to abandon her rebel comrade to Ketsu, Sabine reluctantly returned and docked her shuttle with the Shadow Caster. Meeting face to face, Ketsu discovered that Sabine was determined not to give up the courier droid. She offered to split the bounty but Wren was not interested in profits and reiterated her devotion to the Rebel cause. Onyo was skeptical that the rebellion would succeed and responded that she was solely concerned with her own survival. After a tense discussion, the two former friends reconciled and Sabine forgave Ketsu for abandoning her.
Their reunion was however interrupted by the arrival of an Imperial Arquitens-class command cruiser, which had responded to the theft of the shuttle. Sabine quickly improvised an escape plan which involved exploding the shuttle to create a distraction that would allow the rebels, Ketsu, and EG-86 to escape on the Shadow Caster. Ketsu cooperated with Sabine's plan and personally evacuated her old friend after Sabine was knocked out by an Imperial laser blast. Sabine's plan succeeded and they managed to escape in Ketsu's starship.
Following their escape, Ketsu and the rebels traveled to Havoc Outpost where they delivered EG-86 to a group of Alderaanian rebels that included the astromech droid R2-D2. Ketsu then brought her rebel allies back to Garel. Due to her efforts in helping the rebels to deliver EG-86, Ketsu was thanked by Phoenix Leader Hera Syndulla, the leader of Sabine's rebel cell. Before departing, Sabine told Onyo that she would always be welcome in the rebellion. Ketsu then departed on the Shadow Caster.
Ketsu attended a briefing on the captured Imperial light carrier that had become the Phoenix Squadron's headquarters. By cross-referencing several Galactic Republic and Lasat maps, the rebels found that the planet Berzite's moon in the Yost system was a prospective candidate for a rebel base. Ketsu advocated setting up a base on Berzite's moon on the grounds that the Empire did not have a presence there. However, the rebels were unable to make the trip since the Yost system was a few parsecs away and their cruiser-carrier was running low on fuel.
Sabine, who had been studying Imperial fleet movements, mentioned that an Imperial fuel shipment was arriving at Horizon Base. Commander Jun Sato approved of the plan and sent the Spectres to steal the fuel. When the Phoenix fleet came under attack from Imperial forces under Admiral Kassius Konstantine, Onyo used the Shadow Caster to clear a path for the rebel starship, the Ghost, to land safely in one of the carrier's hangar bays.
10 - Besa Dii (Besadii) Hutt
Ketsu Onyo was a close friend of Sabine Wren, when they both escaped from the Imperial Academy, Ketsu helped her friend. After helping Wren escape, the two became bounty hunters and hoped to work for the Black Sun crime syndicate. According to Sabine, Ketsu then got "greedy", left her for dead, and went to join the Black Sun by herself. As a bounty hunter in the service of Black Sun, Ketsu was ruthless, self-centered, and goal-oriented.
Despite her mercenary streak, Ketsu still could not bring herself to kill her former friend Sabine during a mission to obtain the GNK-series power droid EG-86. When Sabine chose to forgive her, Ketsu responded well to her friend's grace and admired Sabine's team spirit and devotion to the rebellion. She helped her formerly estranged friend to escape the Empire and deliver EG-86 to the rebellion.
Later, Ketsu decided to assist the rebels and recommended the Yost system as a prospective location for establishing a rebel base. When the rebels came under attack from Imperial forces, Ketsu sprung to the aid of her rebel friends.