The ossokata refers a lawsuit body of the Kamakura bakufu (Japanese feudal government headed by a shogun) and the Muromachi bakufu. It took charge of the retrials and direct appeals (to a senior official without going through the normal formalities).
It was established in 1264, as a special section that handled direct appeal, and so on, previously handled by Hikitsukeshu (Co-adjustor of the High Court) where the first trials were examined. Ossotonin (the head of legal institutions) and two or three Ossobugyo (temporary positions in charge of retrials and accepting appeals) from Hikitsukeshu were in commission (according to "Kanto hyojo den" (an annual listing of personnel for the years 1226 and 1232 to 1284) and so on, Ossotonin might be a part of Ossobugyo in a broad sense). However, among Hikitsukeshu, particularly joshu (the head) or second-tier vassal, except regency and rensho (assistant to regents), were customarily appointed as ossotonin; for example, the first ossotonin were Sanetoki KANEZAWA and Yasumori ADACHI. Meanwhile, ossobugyo were chosen from Hikitsukeshu, except for regency, rensho and ossotonin, for each trial. They took charge of practical business for a trial, under the supervision of the ossotonin.
Then, the ossokata, an institution to handle adverse claims to a judicial decision, was excluded when the Hojo clan Tokuso (the patrimonial head of the main branch of the Hojo clan) seized the lawsuit authority. It was abolished at the enforcement of Einin no Tokuseirei (a debt cancellation order). In the next year, it was reestablished with Yukifuji NIKAIDO and SETTSU no Dogen as ossotonin upon the repeal of the Tokuseirei. However, Tokuso tried to control lawsuits including direct appeals; for example, five Miuchibito (private vassals) of Tokuso Sadatoki HOJO were ordered to take charge to a direct appeal in 1300.
The ossobugyo was organized in the Imperial Court during the period in which Emperor Fushimi had the control of the government from 1287 to 1298), and the ossokata and ossobugyo were organized in the early Muromachi bakufu. However, their details are unknown. They were thought to have disappeared as an organization and post during the end of the period of the Northern and Southern Courts.