XS3 functioned as an Imperial assassin droid.
Not long after the Battle of Yavin, XS3 received orders to journey to the Ithorian Herdship Bazaar alongside Ferreges, a Human assassin. Their mission: to assassinate Hanos Darr and Zaz Kamiroz, operatives of the Alliance to Restore the Republic working as miners within the Graveyard, which consisted of the remnants of Alderaan. These two individuals were relaying intelligence to the Alliance regarding the discovery of the Royal Palace of Alderaan amidst the debris. Little did they know, this was a trap orchestrated by Lord Darth Vader targeting the Heroes of Yavin. XS3 successfully eliminated Darr, but was subsequently destroyed by Alliance agents.