Lo and Li had been coming to their beach cottage in Ember Island since they were infants and once their parents died, they inherited the building. When life in the Fire Nation Capital became too hectic, the twins escaped there in order to relax. Lo and Li were both appointed as Azula's firebending mentors when she was a child.
During 100 AG, they accompanied the Fire Nation princess on her journey to the Earth Kingdom to retrieve Prince Zuko. After the prince managed to escape, Lo and Li advised Azula to abandon the Royal Procession in favor of a smaller elite group to better increase her chances of capturing her fugitive brother and uncle.
The duo later presided over a rally held at the Fire Nation Capital's Royal Plaza, where they boastfully declared victory over the Earth Kingdom due to the efforts of Azula and the newly returned Prince Zuko.
Later, Zuko, Mai, Ty Lee, and Azula stayed with the sisters on Ember Island where they owned their small but comfortable beach house. While sharing a meal with the teenagers, the sisters mentioned that the beach had special "powers" and that it supposedly changed people, smoothing even the roughest edges. After sharing this wisdom, they clapped their hands and announced that they were going to the beach, removing their outer garments, much to the displeasure and disgust of the others. Later on, Lo and Li further introduced the island to the teenagers, bringing them to an arcade in the hopes of getting them to have some fun.
Much later, after Fire Lord Ozai appointed himself as the Phoenix King, Lo and Li appeared to Azula, who was to be coronated as Fire Lord. In light of her frantic purging of the Royal Palacestaff, they expressed their concern for Azula's welfare and suggested postponing her coronation. However, the princess misinterpreted their remark as having lack of faith in her abilities to rule, and consequently ordered the twins to fight an Agni Kai. Upon remarking that they were not firebenders, Azula promptly banished Lo. However, since the princess pointed at Li while giving the order, the twin sisters were left in confusion as to who was banished and who was allowed to remain at the palace.
The small triangle that was present on both Lo and Li's hair bands is the alchemical symbol for fire.
Lo and Li are one of five pairs of twins in either series, with Poi and Ping, Desna and Eska, Wei and Wing, and Hundun and his brother being the other four. However, they are the only pair of twins to both be nonbenders.