|"I think this one likes me."|
|— Bumi to his family and Korra upon meeting Bum-Ju.|
Several dragonfly bunny spirits, including Bum-Ju, played with Jinora at the Eastern Air Temple. Although the young airbender could see them, the spirits remained invisible to the others until Jinora urged them to appear under Kya's insistence. Bum-Ju and the other spirits led Jinora and her group to the ancient meditation circle away from the temple grounds, where Bumi officially met the spirit and named him. After their brief meeting, Bum-Ju fled along with the other dragonfly bunny spirits after Tenzin performed a spiritual cleansing ritual on the grounds, which attracted a colony of dark spirits from underground.
Bum-Ju reunited with Bumi following Avatar Korra's defeat of Dark Avatar Unalaq during the Harmonic Convergence of 171 AG. Soon after, the two witnessed the Avatar address the Southern Water Tribe to announce the end of the Water Tribe Civil War and happily listened as she declared her decision to keep the spirit portals open.
Soon after, Bum-Ju traveled with Bumi to Air Temple Island and fled from the retired commander when he attempted to dress him in a hand-knitted pink sweater. Bum-Ju attempted to keep Bumi from falling off a cliff in his attempt to reach the spirit, but was unsuccessful, witnessing as Bumi fell and began to airbend.
Bum-Ju joined Bumi and Team Avatar in their search for airbenders to recruit as part of the Air Nation, keeping the retired commander company while the group traveled across the Earth Kingdom aboard a Future Industries airship. Bum-Ju was with the team when they ambushed two Royal Earthbender Guards in order to access the military compound beneath the Earth Queen's Temple in Ba Sing Se where airbenders were held captive by the Dai Li.
Bum-Ju followed Bumi to the Northern Air Temple, where his owner placed him over his face to mock Tenzin's lessons as boring. Later, as Bumi was venting his frustrations to Bum-Ju, the spirit appeared to disagree with him, causing the airbender to reject his thoughts as his opinion. Bum-Ju soon got a message from a spirit bird, which Bumi correctly interpreted as a message from Jinora which indicated she was in trouble. He went with his owner as he alerted the other airbenders of the trouble.
Bum-Ju stayed with Bumi while he returned to Air Temple Island to continue his airbending training there. When Korra arrived, he accompanied Bumi to greet the Avatar and excitedly flapped its wings upon being addressed by the woman.
Bum-Ju retreated to the Spirit World with the other spirits when Kuvira tampered with the spirit vines and attacked Republic City. After the battle's conclusion and the opening of a third spirit portal in the heart of the city, he returned, however, and flew around the portal with the rest of the dragonfly bunny spirits.
While unable to communicate through speech, Bum-Ju's abiding affection for Bumi was evident by the fact that he rarely left the man's side, even taking part in Bumi's mockery of Tenzin's teaching methods. Despite this, Bum-Ju also displayed his own opinions that sometimes clashed with Bumi's, such as refusing to wear the sweater Bumi had knitted for him and not agreeing with the man's frustrations during his airbending training.