Oshi, which was a castle under the control of the Hōjō clan, was attacked by senior Toyotomi retainer Ishida Mitsunari. Throughout this siege, Mitsunari used a prior strategy of Toyotomi Hideyoshi, that of diverting a river to flood the whole castle area. Yet, the defenders under the Hojo retainers Narita clan held out until the fall of the Hojo stronghold Odawara.