Haru was born to Tyro and his wife in 83 AG and was taught earthbending by his father.
When the Fire Nation invaded their village in 94 AG, Haru witnessed his father and the other earthbenders fight back, despite being outnumbered, and ultimately led away, leaving him alone with his mother. To ensure his safety, Haru was forbidden from earthbending by his mother, although he continued to practice in secret, as a way to feel close to his father.
During the late fall of 99 AG, as Haru was practicing alone, AvatarAang and his friends stumbled upon him. Later, when Haru and Katara struck up a kinship over shared experiences, they came upon a villager trapped under a rock slide. Haru aided him through earthbending, but the old man betrayed him to the Fire Nation soldiers and the young earthbender was taken into custody.
Aang and Sokka helped engineer Katara's false arrest for earthbending so she would be taken to the shipyard. There, she and Haru helped stir up a mass prison rebellion and escape. Reunited with his father and reinforced by fellow earthbenders, Haru had a chance to drive the Fire Nation away from his home.
Following their escape, Haru and his father indeed helped to liberate their village from Fire Nation control as a part of the Earth Kingdom rebellions.
Day of the Black Sun
Haru was one of many familiar but noticeably distinct faces recruited by Sokka to help in the invasion of the Fire Nation on the Day of Black Sun: he now had a mustache and goatee. Haru and his father were part of the ground forces attacking the Fire Nation capital. When the submarines were destroyed, the warriors decided to surrender; Haru promised Tyro that they would return to rescue them. The young people, namely Aang, Katara, Sokka, Toph, Teo, The Duke, and Haru, escaped on Appa and traveled to the Western Air Temple.
Haru befriended both Teo and The Duke after the invasion, and upon arrival at the Western Air Temple, he and his two friends began to explore the sanctuary. They found it to be the perfect place to hang out and for Haru to practice earthbending. While staying at the temple, Haru took part in numerous activities with the team, including spectating at a "swordbending" match, practicing his bending, and joining Sokka's "Bendless Boomerang Club" after he decided to open it up to the whole team.
Haru stuck with Aang's group until Azula and an air fleet attacked the temple. He fled along with Hakoda and his friends while Aang's group flew off on Appa. He later reunited with them during Zuko's coronation after the Hundred Year War ended, finally together with his father once again.
Haru was a skilled earthbender. He preferred earthbending with his hands unlike most earthbenders, who preferred to earthbend with their feet. He and four other earthbenders, including Tyro, created a shield strong enough to withstand a combined blast from several firebenders. Together, he and Tyro were able to compress a large amount of coal into a single projectile, a difficult feat to accomplish.
Haru (春, はる) in Japanese means the season "spring", which correlates with spring being the dominant season for earthbenders.
In The Last Airbender, Team Avatar was captured by the Fire Nation after trying to rescue a young earthbender from Fire Nation troops, but they failed and were placed with him and his father in a compound where the earthbenders from his village were interned. He reunited with his father and threw the first blow in the liberation of his village after an inspirational speech by Aang. Although the boy was never named and was significantly younger than Haru, his story could be easily identified as that of "Imprisoned".
During his Day of Black Sun mission briefing, Sokka humorously said that Haru "now [had] a mustache", an inside joke about Haru lacking facial hair during their first meeting.