Sagashi was born in the southern Earth Kingdom in 132 AG. His mother was of Earth ancestry and an earthbender, while his father was a waterbender who had moved from the South Pole to pursue business interests. Sagashi received his mother's bending traits and discovered his earthbending skills when he was five years old.
In 138 AG, Sagashi's family was forced to relocate to Republic City as his father's business merged into operating interests in the United Republic's capital. Sagashi continued his earthbending training at a city school; here, he encountered future pro-bending rival, Miaka, but the two rarely interacted.
At age eleven, Sagashi and his parents were nearly killed while sailing along the United Republic coast; a storm system took control of their ship during a fishing trip, with estimated winds of ninety miles per hour and driving rain. However, a solid sailing job by their ship's captain was able to navigate them out of the storm and back to the Republic City docks.
Five years later, having reached the age of sixteen, Sagashi was considered an adult in his family. A day later, he went out and applied for a job at a city gym near the Pro-bending Arena. He was hired not too long thereafter, giving him his first job.
One day during his break, Sagashi took a walk over to the pro-bending arena as test matches were starting. Here, he met firebender Gitsu and waterbender Kuska, who were sitting with each other and discussing the possibility of a team. 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.
Sagashi joined Gitsu and Kuska in 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.
Sagashi was forced to step up for a teammate early in the round, as Kuska struggled mightily. However, he took his defense a bit too far when he hit waterbender Halak in the head with an earth coin, costing him one zone. He then had to hold strong and defend against attacks. He then teamed up with his waterbender and forced Halak and earthbender Miaka back a zone. Late in the round, he lost territory which allowed the Winged Lemurs an advance back a zone after losing momentum. He continued to hold up the best he could as the match wore on, his team seemingly losing the round late due to penalties and other blows, but was left ecstatic when Kuska knocked Halak out of the ring, giving his team the first-round victory.
Sagashi is a true team leader, knowing that he has a younger team on his hands. He helps to get the team on the right path to victory, taking a somewhat softer personality, somewhat contrary to a typical earthbender's personality. He is willing to be more comforting with teammates when they feel downbeat about something.
On the ring, however, Sagashi strives to make sure everyone is on the right page, and is more defensive of his teammates, such as when he fired an earth coin at Halak's head in defense of Kuska. This can get him in trouble, and in that case, he was charged with a one-zone penalty for a headshot.
Sagashi is a powerful earthbender and well-versed in its techniques. He does not hesitate to attack with earth coins and, with his power, can drive opponents back multiple zones if he hits the right part.
Sagashi is also quite a fast thinker on his feet, demonstrated when he quickly yelled out strategies about drawing the Winged Lemurs into their weak spot - the corner - late in round one.