He's the first human to be born and raised in Ismo. While living in the village, he was the star trouble maker of the group. He was respected amongst his peers as the leader and bring no end to mischief (for good or bad intentions). After he encounters Susanoo and used the destructive powers of the mech to defeat their enemies attacking the village, the villagers banished the mech and blame it for their misfortune. Yamato can't deal with the superstitious nature of the villagers and opted to leave with his best friend to see the world. It was his journey not long that would allow him to meet Oto and new friends and enemies. After defeating Orochi, he leaves Susanoo where he once rested in the caves and visits him to talk. Because there's no epilougue, it's assumed that Yamato will still cause some trouble in the village as he used to. He'll also probably end up with Oto and start a life together in the village.

In After War, Yamato is called again to pilot Susanoo when a piece of the Dark Sky Carriage falls near the village and Shuranoo reveals itself. But when Yamato refuses to fight Shuranoo, who is possessed by Mikazuchi, Shuranoo mercilessly slashes at Susanoo and then sends it into the lake where it is rescued and healed by the Dragon Carrier. The renewed Susanoo flies off to find Oto who had been kidnapped by Shuranoo. In the end, Yamato was going to sacrifice himself and Oto (willingly) to defeat Tsukiyomi by flying into the sun. Before they get to the melting point, Mikazuchi appears and tells them that he would pilot Susanoo and that Yamato and Oto should live out their lives. Tears fall from Yamato's eyes as Susanoo looks back at him once more before flying into the sun destroying himself and Tsukiyomi.

(Source: Wikipedia)