Xoni, designated RC-1571, was a member of the elite clone commando squad led by captain Nilo known as Tark Squad, which was part of the Special Operations Brigade of the Galactic Republic in 21 BBY. Xoni was nicknamed by his genetic template and trainer Sarsius Torne after the Thyrsian letter for one.
Xoni, Nilo, Quo and Kupe were Thyrsian mercenaries trained by their genetic template, Sarsius Torne of the Sun Guard, to infiltrate the Grand Army of the Republic as part of a deal made with Zeta Magnus and Palpatine to capture Anakin Skywalker. To ensure obedience, all four mercenaries were implanted with cybernetic control bands. In 21 BBY, Xoni and his squad were sent to assist Jedi General Obi-Wan Kenobi and his apprentices, Anakin Skywalker and Halagad Ventor, in liberating the planet Skye from Zeta Magnus while disguised as a relief team.
Xoni and the rest of the liberation team snuck into Zeta Magnus' fortress through Entyrmion's subterranean tunnel system located beneath the fortress. While in the cave, the liberation team was attacked by multiple Oskan blood eaters created by Zeta Magnus which killed many of their S'kytri guides as well as the Lord of the S'kytri Highland Clans, Klarymére. During the fight with one of the blood eaters, Xoni managed to severe a supportive tendon of its heel, sending the creature to crush down. Later, the commando squad was able to kill the blood eaters with a Class-D detonator, although this action angered Obi-Wan, as he believed it was "affront to life". When the liberation team infiltrated the fortress of Zeta Magnus, Xoni and the rest of Tark Squad led the Jedi commanders into a field of R-TechApp Man Traps. Xoni and his squad revealed to the Jedi that they were allied with Zeta Magnus and left them to be tortured by Magnus and his torture droid. The three Jedi later freed themselves, and while Ventor was chasing Magnus, Kenobi and Skywalker killed Xoni and his squadmates in a fierce battle.
Xoni wore specialised Katarn-class commando armor with a silver finish like the rest of his squad. He used a DC-17m interchangeable rifle with a grappling spike launcher attachment and a vibroknife.