Yamato Takeru was the first human born on the planet Ismo after Earth scientists, fleeing through a black hole, abandoned their ship and emergency capsules there. He grew up in Yakumo Village as a mischievous troublemaker and a natural leader among his peers. His life transformed upon discovering the dormant bio-mechanical mecha Susanoo, buried for a million years, which he awakened. This event coincided with an attack on his village by forces from the space station Death Star Yomi, led by Tsukuyomi. Using Susanoo to defend his home, Takeru was blamed for the resulting destruction and banished by the superstitious villagers. He chose to leave, journeying across Ismo with his best friend Roka.

During his travels, Takeru encountered Oto Tachibana, an undercover agent sent to win his trust, steal Susanoo, and assassinate him. Instead, Oto developed genuine bonds with Takeru and his group, fell in love with him, and defected from her mission, an act that marked her for death by her own people. She later learned she was not biologically related to her brother figure, Mikazuchi, but had been taken from her real mother as a child. Takeru’s journey involved battles against Tsukuyomi’s biomechanical Evil Sky Warriors, piloted by kidnapped children, and a confrontation with the sealed eight-headed dragon Yamata no Orochi. Through combat, his mecha Susanoo evolved into a more powerful form, developing a strong psychic link that responded to Takeru’s thoughts and emotions. The dark spirit of Orochi within Susanoo was purged by a sacrificial act that used the creature’s energy to revive Takeru after a fatal encounter. After defeating Orochi, Takeru left Susanoo resting in its original cave and returned to a peaceful life in Yakumo Village with Oto and Roka.

Three years later, in the OVA sequel, peace was shattered when the mecha Shuranoo, piloted by a possessed Mikazuchi, attacked Yakumo Village. Takeru reactivated Susanoo to defend his home but was initially overpowered; Susanoo was severely damaged and thrown into a lake. Rescued and healed by a Dragon Carrier, a renewed Susanoo sought to rescue Oto, who had been kidnapped by Shuranoo and absorbed by the parasitic Tsukuyomi. Faced with this threat, Takeru prepared to sacrifice both himself and Oto by piloting Susanoo into the sun to destroy Tsukuyomi permanently. Mikazuchi, freed from possession, intervened at the last moment, took control of Susanoo, and completed the suicidal mission himself, destroying both the mecha and Tsukuyomi, allowing Takeru and Oto to live out their lives together on Ismo.