Yung was an enthusiastic earthbender who was willing to die rather than turn Omashu over to the Fire Nation. As the captain and second-in-command of Omashu's forces, Yung was with his king atop the city's wall when the Fire Nation troops began their siege. In the face of the enemies' forces, Yung asked Bumi for orders, but the king told him that he would do "nothing" and surrendered. The captain, however, disillusioned about his leader and unwilling to simply give up, formed a resistance in order to drive the Fire Nation military out of Omashu. Recruiting able-bodied, like-minded citizens of Omashu, he made the Omashu sewers their base of operations and planned attacks to attempt to remove Fire Nation control of the Earth Kingdom city, thereby reclaiming Omashu for his people.
As the newly returned Team Avatar pondered the whereabouts of Bumi in the captured city, he and his team found earthbender resistance fighters in the midst of an assassination attempt. They had planned to assassinate the governor's wife and daughter by earthbending a rock down one of the delivery slides. This attempt, however, was foiled by Aang, who used his airbending to deflect the rock. Believing them to be the assassins, Mai chased Aang and his friends. Despite the fact that they foiled their plot, Yung and the resistance members helped Team Avatar to escape by earthbending them into the sewers. Once down in the tunnels, Yung explained his frustration at merely surrendering the city without a fight. After hearing his resolve, Aang pointed out that the resistance was outnumbered and unable to win against the Fire Nation, instead suggesting to leave the city "to fight another day". The captain was initially against this plan, but after his subordinates declared that they were convinced by the Avatar's words, Yung hesitantly agreed.
Later, following Sokka's plan, Yung and the resistance used purple pentapus prints to simulate a plague, "pentapox". The governor was fooled and ordered the "ill" to be driven out of Omashu. After they had vacated the city, Yung noticed they had an extra person after he did a head count, and found the governor's son, Tom-Tom, was among them. When Katara called the toddler "cute", Yung pointed out that once the child had grown up, he would join the Fire Nation Army and become a "killer" just like every Fire Nation citizen. Nevertheless, he handed Tom-Tom over to Aang, who eventually took him back.