RC-1571, known as Xoni, served within the Galactic Republic's Special Operations Brigade during 21 BBY. He was a member of Tark Squad, an elite clone commando squad commanded by captain Nilo. His genetic template and trainer, Sarsius Torne, gave him the nickname Xoni, which is the name of the Thyrsian letter for one.
Nilo, Xoni, Quo, and Kupe were Thyrsian mercenaries trained by Sarsius Torne, their genetic template from the Sun Guard. They were tasked with infiltrating the Grand Army of the Republic as part of an agreement between Zeta Magnus and Palpatine to capture Anakin Skywalker. To ensure their loyalty, each mercenary had cybernetic control bands implanted in them. In 21 BBY, Xoni and his squad, disguised as a relief team, were dispatched to aid Jedi General Obi-Wan Kenobi and his apprentices, Anakin Skywalker and Halagad Ventor, in the liberation of the planet Skye from Zeta Magnus.
The liberation team, including Xoni, infiltrated Zeta Magnus' fortress via the subterranean tunnel system of Entyrmion located below the fortress. Within the cave system, the team was ambushed by Zeta Magnus' creations, Oskan blood eaters, which resulted in the deaths of several S'kytri guides and Klarymére, the Lord of the S'kytri Highland Clans. During a fight, Xoni severed a supportive tendon of one blood eater's heel, causing it to collapse. The commando squad later eliminated the blood eaters using a Class-D detonator, an action that Obi-Wan disapproved of, calling it an "affront to life". Upon entering Zeta Magnus' fortress, Xoni and Tark Squad led the Jedi commanders into a field of R-TechApp Man Traps. Xoni and his squad then revealed their alliance with Zeta Magnus, leaving the Jedi to be tortured by Magnus and his torture droid. The three Jedi eventually escaped, and while Ventor pursued Magnus, Kenobi and Skywalker engaged Xoni and his squadmates in a battle that resulted in their death.
Like the rest of his squad, Xoni wore Katarn-class commando armor with a silver coating. He was armed with a DC-17m interchangeable rifle equipped with a grappling spike launcher attachment, and a vibroknife.