Heir of Kazusa

…During the Ten'yō era (1144-45), he allied with the Mokudai (deputy governor) and attempted to obstruct the invasion of Oba no Mikuriya in the same province, and around the same time, he also plundered the Soma no Mikuriya in Shimousa. As Yoshitomo was also known as Kazusa Goshoji, it is assumed that he also had influence in the Boso region. He went to Kyoto and became Shimotsuke no Kami, and in 1156 (Hogen 1) during the Hogen Rebellion (Hogen 1), he fought on the side of Emperor Goshirakawa, just like Taira no Kiyomori, and after the rebellion, he killed his father Tameyoshi, his brothers, and other members of the Minamoto clan who were on the side of Emperor Sutoku. …

*Some of the terminology explanations that refer to "Kazusa Heir" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…天養年間(1144‐45)目代（もくだい）と結んで同国大庭御厨（おおばのみくりや）の押妨を企て，さらに同じころ下総相馬（そうま）御厨をも掠領した。義朝には上総御曹司の異名があるところから，房総地域にも勢力を扶植していたと推測される。上京して下野守となり，1156年(保元1)保元の乱で平清盛と同様後白河天皇方として戦い，乱後父為義，兄弟以下崇徳上皇方の源氏一族を斬った。…

※「上総御曹司」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報