Sonnō jōi
Yoshihara was born in Satsuma Domain (modern Kagoshima Prefecture as the son of a samurai retainer to the Shimazu clan. As a youth, he was the youngest of the "Sonnō jōi" samurai to participate in the "Terada-ya Incident", an assassination attempt against Sakamoto Ryōma at the Terada-ya inn in Kyoto. During the Anglo-Satsuma War of 1863, he fought alongside Ōyama Iwao and Saigō Tsugumichi. After the end of the conflict, he was sent to Edo, and then to Hakodate, where he was ordered to study "rangaku" and western customs under Takeda Ayasaburō. He then went to Yokohama to learn English from Samuel Robbins Brown.