In the 1590 Odawara Campaign, Hideyoshi ordered Ishida Mitsunari to take Oshi Castle, and he besieged it with some 23,000 men. To flood the marsh-girt castle he built the roughly 28 km 'Ishida embankment' in just days, diverting the Tone and Ara rivers. But the dike breached — aided by the defenders' night raids — and the water attack failed. The castle did not fall until Odawara surrendered, a blow to Mitsunari's reputation as a field commander, while the spirited defense by acting castellan Narita Nagachika and his kinswoman Kai-hime lives on as the tale 'Nobou no Shiro.'

During Toyotomi Hideyoshi's 1590 Siege of Odawara, Oshi Castle came under a massive flood attack led by Ishida Mitsunari. Defended by a small garrison under Narita Ujinaga, the castle—surrounded by marshland that gave it a natural advantage—never fell, earning it the nickname "the Floating Castle" and standing out as an unusual episode within Hideyoshi's campaign to unify Japan.