Lifespan: 15xx to Eiroku 12 (1569) or Genki 3 (1572)
Rank: bushō; chief retainer of the Tosa-Ichijō clan
Lord: Ichijō Kanesada
Father: Ichijō Norifusa
Siblings: Ichijō Fusaie, Sōzan
Wife: Older sister of Doi Kiyoyoshi
Doi Sōzan served as a bushō during the Sengoku period. Sōzan was the chief elder of the Tosa-Ichijō clan. He is commonly known as Ōmi-no-kami Ietada. He was the lord of Imaki Castle near Nakamura Castle (also known as Tamematsu Castle). Sōzan was the founder of the Tosa-Imaki clan.
His son was Tosa Awa-no-kami Iemichi, later known as Imaki Izu-no-kami Michioki, lord of Kitanokawa Castle in the former village of Nishi-Tosa.
As the chief elder of the Tosa-Ichijō clan, Sōzan served as a master of internal affairs and diplomacy. It was said that Doi Sōzan was the guardian deity of the Ichijō clan, and it was known even in other provinces that as long as Sōzan is present, no one would lay a hand on the Ichijō.
Doi Kiyoyoshi, a well-known commander in Iyo Province and one of the Fifteen Generals of the Saionji who served as lord of Ōmori Castle in Iyo, was Sōzan’s brother-in-law. Sōzan fell in love with Kiyoyoshi’s older sister, and was adopted by the Iyo-Doi clan. Sōzan was the son of Ichijō Norifusa, the founder of the Tosa-Ichijō clan who held the role as kanpaku, or Chief Advisor to the Emperor. Sōzan was also the younger brother of Ichijō Fusaie, the second head of the clan. This history enabled him to become the chief retainer in the clan.
Sōzan worked desperately to support his lord’s family which weakened in the face of attacks from Chōsokabe Motochika, but he was executed at the hands of Ichijō Kanesada, his lord and fifth head of the clan. According to one account, Sōzan was executed in return for admonishing Kanesada’s behavior. According to another account, Sōzan was the subject of frequent attempts to lure him by Motochika, and after those on the side of Motochika gave up and spread rumors, Kanesada suspected Sōzan of wrongdoing and executed him. Based on another theory, Sōzan was assassinated by a member of the Chōsokabe clan who misrepresented himself under the name of Kanesada. In the background of this event, there was a strange love story between Kanesada and a strikingly beautiful woman named Oyuki from the village of Hirata, as well as numerous plots by certain retainers of the Ichijō clan who colluded with the Chōsokabe clan, but the details are unclear.