In the following months, Mako joined the Republic City Police Force, where he steadily rose up from being a beat cop to a detective. He joined his friends in an effort to stop Unalaq and Vaatu from merging. A few weeks after Harmonic Convergence, he rejoined Team Avatar in their search for new airbenders. However, they stopped when the Red Lotus attempted to kidnap Korra in Zaofu, instead working to bring down the anarchist organization.
After taking down the Red Lotus, Mako returned to his work as a police officer and was later appointed as Prince Wu's bodyguard, a position he continued in after the latter's coronation as Earth King.
Mako was born the son of an Earth Kingdomman named San and Naoki, a Fire Nationwoman, two years before Bolin. When he was eight, Mako witnessed his parents being killed by a firebender, leaving Bolin, his younger brother, as his only immediate family and his treasured red scarf as the sole memento of his father. Being the elder brother, with no knowledge of his relatives, he was forced to take on adult responsibilities from that point on, depriving him of the majority of his childhood.
As an orphan, Mako did whatever was necessary in order to survive along with his brother. He often resorted to his firebending to protect himself and Bolin on the streets. Both of them also ran small-time scams during much of their youth. This attitude brought him in contact with the criminal organization known as the Triple Threat Triad, for whom he collected money for bets and ran numbers. Mako even came into close-contact with the leader of the triad, Lightning Bolt Zolt, and was able to learn the techniques of lightning generation and redirection from him.
One day in 167 AG, during Mako's involvement with the Triple Threat Triad, the young firebender and his brother attempted to pull off a scam on an elderly woman. Posing as a thief, he ran toward the woman from behind and grabbed her purse, before leaving her sight by entering a side alley. When Bolin pretended to chase after him and fight, Mako willingly gave the purse to his brother, deceiving the woman into thinking that the young earthbender had stopped a thief. Bolin returned to Mako with a reward of two yuans and a loaf of bread he had stolen from the old woman; after Bolin gave a piece of the loaf to his brother, Mako reminded him that they had not eaten anything the day before.
Later that day, Mako went to the Triple Threat Triad headquarters with his brother and saw Shady Shin bribe Toza, a pro-bender. When Bolin expressed his disappointment about seeing Toza act this way, Mako became upset – Toza should be happy about being paid, Mako opined; after all, there had been no one to mourn for their losses when their parents died and had left them to fend for themselves, and that one must "hustle or be hustled". Afterward, Shin told them that if they did not acquire enough bets to recover the ten thousand yuans given to Toza, he would abandon Mako and Bolin on the streets, after which the two brothers speedily departed.
While the brothers were collecting bets at a pet shop, a fire ferret escaped and was restrained by its owner, Mr. Feng, because it was to be fed to a pythonaconda. Mako stopped Bolin from buying it as they could not afford to feed it, and felt his younger brother needed to toughen up and realize that bigger animals consumed those smaller than them. Mako collected the owner's bet while Bolin talked to Toza about that night's match; the firebender chastised him because he believed that doing so would get them in trouble with Shady Shin. Bolin angrily responded that Mako was being mean and walked away, leaving Mako to sigh.
That night, after Bolin broke into the pet shop to steal the fire ferret, he was strangled by the pythonaconda, but Mako arrived and yanked the snake away. After again criticizing his brother for getting into stupid situations, the two left, but, at Bolin's urging, with the fire ferret whom the earthbender named Pabu. Mako warned Bolin that Pabu's food would come out of half of his money.
Later that night, Mako and Bolin attended Toza's match, sitting in the same booth as Zolt and Shady Shin. However, when Toza won and Bolin revealed that he had encouraged the pro-bender to not to throw the match, Mako urged his brother to run from an irritated Shin. The brothers were eventually cornered by Shady Shin and two other gangsters and forced into the defensive until Toza helped bring the fight to a standstill and Zolt eventually broke it off completely. Impressed with the brothers' abilities, Mako and Bolin were offered the chance by Toza to live at the gym and train under him to become pro-benders. While Bolin was immediately won over by the idea, Mako doubted and Shady Shin used this to appeal to the young firebender's pragmatic nature and point out that he needed to protect his younger brother. Mako agreed with that assessment and used it as a reasoning to take Toza's offer for a chance at a more honest life. When Bolin wanted to celebrate the abandonment of their criminal lives, Mako reminded him they had to save what little money they had at that point, though due to Bolin betting on a Boar-q-pine victory, they had more than enough to celebrate with.
Acknowledging the dangerous nature and moral ambiguity of their past, Mako was determined never to return to that life and explicitly forbade Bolin from associating with the Triple Threats in any way. Under Toza's tutelage, Mako and his brother began competing in the Pro-bending Tournament and they were also offered the chance to work odd jobs to pay rent which allowed them to focus on the sport. Mako eventually became the captain of a pro-bending team, the Fire Ferrets, which included his brother and his friend Hasook.