Though two years younger than Obi-Wan Kenobi, Tachi was just as powerful in her skills with lightsaber and the Force. As an adolescent, she had a very tomboyish attitude, even while considered attractive by her male peers. As with Kenobi, Tachi had a rivalry with fellow Jedi trainee Bruck Chun.
The first time Tachi spoke to Kenobi, she had already learned of his temporary leave from the Jedi Order to help the adolescents on Melida/Daan to halt the civil war on the planet, and was angry with him, calling him an embarrassment to all potential Padawans (this was before she was chosen as a Padawan herself). Later on, she helped him trace Bruck Chun's connection in Xanatos' infiltration of the Jedi Temple.
A few months following the Xanatos incident, Jedi Master Adi Gallia chose Tachi to be her Padawan learner. The two accompanied Kenobi and his master Qui-Gon Jinn on several missions to planets such as Kegan, Simpla-12, and Sorrus. With Adi Gallia, Tachi helped Kenobi rescue Jinn from the Force-obsessed scientist Jenna Zan Arbor. Later, Kenobi saved her from the bounty hunter Ona Nobis. Before this mission, Tachi was a headstrong and impatient Padawan, having difficulty understanding when to refrain from a fight, but learning from Kenobi's example, she became more patient and prudent .
It was not until a few years into their friendship that Tachi and Kenobi realized their true feelings for each other. Along with their masters, the two were again sent on a mission together: this time to save a boy, Talesan Fry, from bounty hunters on the planet Cirrus. After crashing on the planet Quadrant Seven, the masters sent the Padawans to hide in the nearby caves in order to protect Fry. During the time they spent in the caves, Tachi and Kenobi's bickering briefly allowed them to express their feelings for each other, but they decided to put their focus on the mission. At one point in the mission, the Padawans and Fry were on board a ship rigged to blow up if it exited hyperspace. It was during this time of potential death that Tachi and Kenobi truly recognized their feelings and after finding a way to land the ship safely, they confirmed that they were in love. They agreed to discuss their situation more in depth after the mission was over. After putting Fry into safe hands (following the death of his parents at the hands of the bounty hunter Magus), the two agreed to abandon their love, after a talk with Jinn and Yoda about the consequences of Jinn's love for the late Jedi Master Tahl. Tachi and Kenobi vowed never to speak of their love again. However, this decision led to the gradual drifting of their friendship.
Shortly after the Invasion of Naboo, Tachi and Adi Gallia had a major disagreement, which led to Gallia dismissing her informally as Padawan, and Tachi leaving the Jedi Order. She joined the slave trader Krayn and renamed herself Zora. Tachi remained a part of his operations as his right-hand person until she briefly encountered Kenobi and his new apprentice, Anakin Skywalker. Kenobi, like most other Jedi, had believed that Tachi was a traitor. However, after the encounter with Zora and lashing out at her, he later searched his feelings and realized the truth that Tachi would never willingly betray the Jedi. This was confirmed by the Jedi High Council, revealing that Tachi's "disagreement" with Adi Gallia and her "dismissal" from the Jedi Order were all part of an intricate plan set up by the Council to overthrow Krayn's slave operations. Soon after this revelation, Skywalker, who was captured earlier and made a slave, inadvertently disclosed the true identity of "Zora," and Krayn imprisoned her with Skywalker. Working together, the two Jedi convinced the slaves to organize a revolt. With Kenobi's help from the outside, they succeeded in destroying Krayn's operations, ending with Skywalker killing the slaver. Her undercover mission finished, Tachi was welcomed back to the Jedi Order.
Upon her return, Tachi became a Jedi Knight, and she took Ferus Olin as her Padawan learner. They went on a number of missions together, along with Kenobi and Skywalker, to places such as Radnor and Euceron. One mission was when Tachi and Kenobi's apprentices infiltrated and posed as students at the Leadership School on Andara in order to discover the background behind the kidnapped son of a Senator. Tachi and Kenobi's part of the mission involved them posing as the king and queen of Cortella considering the enrollment of their "children" at the school.
Other missions that Tachi and Olin took included their rescue of Kenobi and Skywalker from Jenna Zan Arbor on Vanqor, their investigation of Zan Arbor, Roy Teda, and Granta Omega on Romin, and their investigation of Zan Arbor's Blacwater Systems laboratory on Falleen, before a crucial mission on Coruscant.
Following Omega, Zan Arbor, and Teda to the capital world, Tachi, Olin, Kenobi, and Skywalker discovered their plans to assassinate hundreds of Senators and dignitaries, including Supreme Chancellor Palpatine himself, using assassin droids assigned to specific targets. Tachi, Kenobi and Skywalker went off to find the trio of criminals while Olin valiantly protected the Chancellor and Senators from the droids (though there were some two dozen casualties). Following the death of Teda and another escape by Omega and Zan Arbor, the two master and apprentice pairs headed for Korriban, where the two criminals were reported to have been seen.
Along with Soara Amtana, Ry-Gaul, and their respective apprentices, Darra Thel- Tanis and Tru Veld, the investigation of the Jedi in Korriban's capital of Dreshdae led them to Omega and Zan Arbor in the Valley of the Dark Lords. It was during this fateful mission that Thel-Tanis was killed by Omega. After completing the mission (which resulted in Omega's death and Zan Arbor's escape) and returning to the Temple, Olin expressed his guilt over Thel-Tanis' death and announced that he was resigning from the Jedi Order.
After Olin's resignation, Tachi never took another Padawan. She mostly worked on solo missions and befriended the pilot Nym and his squadron, the Lok Revenants. Tachi helped them defeat the Trade Federation numerous times, but eventually she parted ways with them. However, Tachi fought alongside them again, with Adi Gallia and a number of other Jedi pilots, using the new Delta-7 Aethersprie starfighters. She was introduced to the Galactic Republic's new Clone Army and guarded the Republic transports with Gallia in space above Geonosis, where Kenobi, Skywalker, and Senator Padme Amidala were being held by Count Dooku's Confederacy of Independant Systems. Prior to the Batle of Geonosis, Tachi aided her former master Adi Gallia in thwarting Cavik Toth's fleet of Hex Deployers. This was the start of the Clone Wars.
Following the Battle of Geonosis, Tachi went to Kamino to investigate the sighting of Slave I, despite its owner Jango Fett having been killed by Mace Windu in the battle. While on Kamino, Tachi almost discovered Fett's son, Boba, but having been forewarned that a Jedi was arriving, he managed to elude her.
In 20 BBY, over two years into the Clone Wars, Tachi reunited with Kenobi and Skywalker, as well as Padmé Amidala, to go to the planet Genian. The Separatists were after an important codebreaking mechanism invented by Talesan Fry, whom Tachi and Kenobi had met decades earlier. Fry was now the founder of a very wealthy business on Genian, a world that remained neutral during the war. Reuniting with Fry brought back old memories to Kenobi and Tachi of the feelings that they once had for each other. After convincing Fry to give the device to the Republic, they were attacked by someone else from the past, the bounty hunter Magus, who had killed Fry's parents.
Fry accompanied the Jedi and Senator Amidala to Azure, where the Republic was fighting off more Separatists. While Kenobi, Skywalker, and Fry fought off the attack led by Magus (who was working for the Corporate Alliance), Tachi and Amidala took a starfighter of their own to go after Magus himself. Upon reaching Magus, Tachi made a desperate leap and landed on his starfighter, leaving Amidala to fly the ship herself. Tachi was able to break into Magus’ ship and fight him off, which resulted in the ship's crash landing.
When the Jedi found them, Fry already had Magus held at gunpoint, while Tachi was fatally injured, having been shot by Magus. Kenobi tried to save her, but she stopped him knowing she was dying, and the two expressed their love for each other yet again. Tachi handed him the blue warming crystal she had from their first mission with Fry, telling Obi-Wan that she would always be with him, and then passed on. As Obi-Wan came close to the dark side, he held his lightsaber blade to Magus' throat; however, he regained control before it was too late, sparing the bounty hunter. Later Skywalker wondered about Kenobi's feelings for Tachi, but incorrectly came to the conclusion that his master did not love Tachi because he did not kill her murderer. Kenobi had learned to love with an open heart, and could live with losing Tachi. The memory of a dedicated Jedi and dear friend lived on with Kenobi and he continued to miss her just as constantly and intently as he went into exile to watch over young Luke Skywalker on Tatooine following the Great Jedi Purge.