Okioshio Castle is located on the 370-meter Mount Ojioyama, north of the center of Himeji city.

A minor clan of Harima Province, under Akamatsu Norimura (1277-1350) the clan rose to prominence during the Kamakura period serving the Rokuhara Tandai, and sided with Emperor Go-Daigo during the Kenmu restoration to overthrow the Kamakura shogunate.

Akamatsu Norimura drove the Hōjō clan from Kyoto; however, afterwards he received scant rewards from Emperor Go-Daigo for his efforts, and was even relieved of his title of shugo of Harima Province.

Akamatsu Mitsusuke assassinated Ashikaga Yoshinori at a banquet in Kyoto, but his revolt was ultimately unsuccessful and the clan lost much of its territory.

At an elevation of 300 meters, it was necessary to climb up a steep and winding road with a length of over 1.8 kilometers to reach the inner Bailey at the summit.