He served as Lord of Chikugo and Higo provinces in Kyushu and was favored by Kiyomori Taira. When Takanao Kikuchi and others rose in arms in Kyushu in response to the call of Yoritomo Minamoto (1180), he defeated them by cutting their supply route in Higo and returned to Kyoto.
At a report that Yukitsuna Tada revolted at Kawajiri in Settsu Province (Hyogo Prefecture), he led his troops there and found that the report had been a false one. While on the way back to Kyoto, he met Munemori and other Tairas retreating westward.
Although he tried to dissuade Munemori from retreating, Munemori would not listen. Sadayoshi then went to Kyoto, moved the remains of Shigemori to Mount Koya and then followed Munemori to Kyushu. In Kyushu, he was attacked by Koreyoshi Ogata and retreated in defeat.
Then he became a Buddhist priest, assuming the name of Iten. He escaped death because Tomotsuna Utsunomiya interceded on his behalf for a pardon by Yoritomo.