Sōga hails from the Land of Asura, sharing a deep childhood bond with Raoh and his younger sister, Reina. He and Reina eventually left their homeland to aid Raoh's campaign for dominance. Serving as chief strategist for the King of Fists Army under Raoh, Sōga wielded the martial art Sūzan Senpū Kyaku (Songshan Whirlwind Kick) and privately desired to reconcile Raoh with his brothers, Toki and Kenshiro, believing their unity was crucial for ultimate supremacy.

During the early rise of Raoh depicted in the Ten no Haoh spin-off, Sōga earned the epithet "Souga the Swift Foot" for his agility. However, he was severely injured by a trap during an escape from Cassandra with Raoh and Reina, resulting in the loss of his right leg, which was replaced with a mechanical prosthesis. Following this injury and an encounter with Ryuga, Sōga abandoned aspects of his humanity, adopting a more ruthless approach to further Raoh's conquest.

Later, combat with Gaiya inflicted a fatal wound upon Sōga, leaving him with only two months to live. Knowing his time was limited, he orchestrated an intricate plan. He staged a fake assassination attempt targeting Raoh, which culminated in Raoh himself delivering the fatal blow and executing Sōga. This sacrifice was designed to instill discipline within the complacent Ken-Oh army. The full conspiracy, including the complicity of Raoh and the supposed assassin, was revealed to Reina after Sōga's death through a letter he had written beforehand.