Ketsu is an old friend of Sabine Wren before joining the Rebel Alliance. Both attended and escaped from the Imperial Academy on Mandalore together to become bounty hunters. But they eventually had a fallout and took different paths. Ketsu became a bounty hunter, contracting with the Black Sun, while Sabine became part of the Rebellion against the Galactic Empire.
Originally, Ketsu was blood sisters with Sabine, nearly family. They were best friends, even joining each other at the Imperial Academy until they both got fed up with the Empire, both resolving to become bounty hunters, join the Black Sun, and get off Mandalore. Until Ketsu got greedy and left her for dead. During this time she became bitter, cold, and selfish. She did not care what anyone was going to do with her targets unless she got paid. After her time with the rebels and reconciling with Sabine, she resolved to see a better future for herself. Finally setting down the right path.
In her debut, At bay twenty-two on Garel, Ketsu waited to reveal a messenger of the rebels and to get the information they had transported in order to sell them to their clients. The courier from Ezra Bridger and Sabine Wren, who wanted to take a GNK energy drill called EG-86 as the same courier in their custody, should be received until Onyo intervened. After brief discussion about the common past of Wren and Onyo and about the further process with the droids, Onyo opened fire on an imperial patrol, which wanted to clear the hangar after its closure for passenger traffic. During the next shooting, Wren was able to get on board the Garel Shuttle 63725 with the EC-86 and her Astromech C1-10P "Chopper" and stole the space ship. Ketsu remained on the ground, but immediately took the pursuit into the orbit with the Shadowcaster.
When the Shadowcaster took the shuttle, Onyo cleared the hypo-space drive of the GX1 Short Haul with Sabine, the courier and chooper on board, and then destroyed the entry hatch so that Chopper was pulled into the vacuum before Wren could compensate for the pressure. Onyo contacted after the first salvo, but did not notice that Chooper remained motionless in vacuum with thrust nozzles and started dismantling the Shadowcaster's weapon systems. Wren did not enter Onyo's offers and Onyo opened the trigger. The missing shots offered Wren time to get the shuttle back on course and collect Chooper. This, however, prevented the head-hunter with the tractor beam of her ship and offered after the salvage of Chopper a change from droide to droid. Sabine agreed, and the two ships docked until an Imperial cruiser landed over the commlink, which in turn announced his docking to the shipped shuttle.
Meanwhile, both in danger, Sabine and Ketsu joined forces to escape the situation and made arrangements to blow up the shuttle to flee with Onyo's ship. After the two ships were undocked, both were trapped in the tractor beam of the Imperial cruiser, until the shuttle closer to the cruiser exploded, causing serious damage to the enemy ship, whereupon the Shadowcaster jumped into the hyperspace and delivered the courier to the agreed meeting point. After returning to Garel and a meeting with the crew's spirit, Onyo did not persuade himself to join the rebel network, but stressed that this decision did not last forever.
Ketsu later came to the aid of the Rebellion when they were looking for a new base, with Ketsu suggesting the Yawst System due to its apparent lack of Imperial activity. Despite her previous reluctance to become involved in the rebellion, Ketsu defended the Ghost from TIE Fighters using the Shadow Caster when Phoenix Squadron was attacked by the Imperial fleet under Admiral Kassius Konstantine.
- Ketsu's design is based on some abandoned concept from the early development of Star Wars: The Force Awakens.
- She is the second Mandalorian character to appear in Star Wars Rebels, followed by Sabine Wren.