Roku found Fang when he was just a baby, not yet hatched from his egg. Fang's parents were gone, so Roku raised the young dragon as his own and they became inseparable.
When Roku's island experienced a massive eruption in 12 BSC, Fang attempted to aid his friend. Even though Roku insisted that he leave, Fang stayed with him the entire time. After initially helping Roku to contain the eruption, Fire LordSozin betrayed Roku, and left him to die. Fang then curled up around Roku to protect him and the two died together when they were overcome by a pyroclastic flow. Fang then entered the Spirit World along with Avatar Roku.
Fang first appeared to Aang when he was attempting to stop Hei Bai from destroying Senlin Village. After Aang discovered he was in his spirit form for the very first time, he was confronted by Fang, who took the young Avatar to the Fire Temple on Crescent Island to see Avatar Roku's statue. Aang found out that Avatar Roku wanted to speak to him about Sozin's Comet and the only time they could talk was during the winter solstice. The dragon then took Aang back to his body. Fang then transported Aang and Roku while the latter talked to the former about the dangers of the Avatar State.
When Aang was comatose after Azula's lightning attack, he had to meet his past four lives. Fang was able to guide Aang to Roku and the two Avatars spoke of the latter's past, although Aang did not remember the incident.
Fang later flew Roku and Aang to the Southern Air Temple in Roku's memories and then the two Avatars saw his living form during his and Roku's final moments.
As a spirit, Fang wielded several abilities common to all those who resided in the Spirit World, such as intangibility and invisibility. Being a dragon, he retained his capacity for flight. However, what really made Fang unique were his telepathic abilities, which he used to communicate with others. Messages were sent using his whiskers. He could not actually transmit speech, but instead sent images and impressions. When Aang first saw Fang, the dragon spirit used his ability to tell Aang that he was Roku's dragon. When they reached the Fire Temple, he used it again to let Aang know when and where he could speak to Roku. Afterwards, he sent Aang back to the real world by flying into Hei Bai's statue, which reawakened Aang's lifeless, meditating shell. The only people known to see Fang in his spiritual form in the mortal world were Aang and General Iroh.