Gatsu was born in Republic City in 133 AG. His parents' roots are not known; it is suspected they had worked for triads in the early days of the United Republic, and had their histories wiped out to cover for their crimes. Nevertheless, Gatsu was raised quietly at home in the large-scale capital.
He discovered his firebending abilities at the age of three, and soon enrolled in firebending classes in the nation. Over time, Gatsu dedicated himself to mastering his bending to the best of his abilities, spending - even against his parents' wishes - late nights training. This work paid off as he was declared a master at age fifteen, graduating from his class.
A year later, with pro-bending starting up test matches, Gatsu decided to take a trek down to the Pro-bending Arena to view them. Here, he met waterbender Kuska. The two talked about their rising interest in the sport, and discussed the possibility of forming a team. Earthbender Sagashi, whose interest had been peaked by viewing the test match, encountered the two and offered to be their earthbender and captain. The three agreed and entered themselves into a test match, naming their team the Aardvark Sloths.
Gatsu, Sagashi and Kuska enjoyed heavy successes in their test match, claiming a three-to-nothing clean sweep. Their success overall earned them a spot in the inaugural match against the Winged Lemurs.
As his teammates lost a zone early, Gatsu held up against a barrage of attacks from the opposition, mostly dealing with Lemur captain Shao Fung. However, opponent earthebender Miaka came at him with an earth coin, sending him back a zone. But later, Gatsu would fight back against Shao Fung, and push him all the way back to the edge of the Lemurs' side of the field. But the Lemurs' captain knocked the firebender back after dodging attacks, costing his team some momentum. However, he held on enough, and eventually, his team won the first round at the last second thanks to Kuska.
Gatsu tends to be more outgoing and friendly toward others. He does not typically hesitate to talk to someone if he sees they are having a problem, and is also open to starting a conversation. However, when asked about his background, he tends to ignore questions, and if he is continuously bothered, he will get a bit aggressive in tone.
On the playing field, Gatsu stays focused while trying to help his teammates out the best he can. Some analysts believe that he should be the captain instead of Sagashi, however, no additional comment was given regarding the matter.
Gatsu is a firebending master. A prodigy thanks to his large training efforts, he is capable of essentially every move short of Avatar-level firebending. The only thing he cannot do otherwise is pull off any other color of fire outside its typical color. Nevertheless, he is a fearsome firebender who is also catching the eyes of United Forces recruits in the city, though he has not been approached. As of now, Gatsu demonstrates his skills in the pro-bending ring, his bending being a critical part of the Aardvark Sloths' win in their test match.