Saitō Dōsan, the formidable "Viper of Mino," governs Mino Province as its daimyo. His greying eyebrows and mustache mark his age, and he typically wears traditional Japanese attire while bearing a katana. Though renowned for his fearsome reputation and seen in battle armor, he reveals kindness and wisdom, especially towards those he holds dear. He becomes a stepfather to Oda Nobuna after her father's demise, recognizing her ambition to unite Japan when others deem her foolish.

Originally a merchant, Dōsan seized power by conquering Mino, transforming it into a prosperous trade center. He initially plotted war against the Oda clan but abandoned this ambition upon recognizing Nobuna's potential and considering Sagara Yoshiharu's insights about the future. He forged an alliance by naming Nobuna his heir and sending his daughter Kicho to serve her. This decision provoked his son Yoshitatsu to rebel. During the coup, Dōsan resolved to fight to the death protecting Nobuna's interests but was persuaded by Yoshiharu to flee. They escaped via river under pursuit from Yoshitatsu's forces until Nobuna's arrival secured their safety, highlighting his willingness for self-sacrifice.

Later, he confronted Yoshiharu after the latter abandoned his duties, advising him to pursue greatness through effort rather than retreat and directing him towards becoming a general, emphasizing self-determination. Subsequently, Dōsan contracted a fatal illness yet chose to lead the defense against Takeda's forces despite the risk, knowing no other commanders were available. He repelled the invasion but succumbed to his illness shortly after Nobuna arrived, his final moments witnessed by her.

His relationships define him. He shares a profound bond with Nobuna as her adoptive father and one of the few who truly comprehends her vision for Japan. He mentors Yoshiharu, offering strategic guidance. His conflict with Yoshitatsu stems from doubts about the latter's lineage and succession, culminating in the rebellion that forced his flight. In lighter moments, he exhibits a lecherous side, particularly during his initial meeting with Nobuna, without overshadowing his serious nature. His romantic past with the equally cunning Danjō further illustrates his complexity.