During the fierce sword fighting in the Tenmaya Incident of December 1867, along with other members including Hajime SAITO, Oishi was assigned as a bodyguard for a feudal retainer of Kishu Domain Kyutaro MIURA.
また12月の天満屋事件では乱闘の斬り合いの中、紀州藩士　三浦休太郎の護衛の任務を斎藤一らと共に果たしている。