In June 1590, Ishida Mitsunari led a 20,000-man army to take Oshi Castle. Mitsunari started to build a large embankment, and completed this embankment in a week. He placed his headquarter at the top of old tomb near the castle, and ordered to pour water into the castle. In a moment Oshi castle was filled with water, and inside people had to evacuate to higher place. The moats around the castle rejected the water attack. The embarkaments built by Toyotomi's men were used against them. Kaihime broke the dikes near the castle, causing massive damage to the Toyotomi army. Owing to lack of foresight and planning, Mitsunari troops was devastated by the water attack. Kai was said to have volunteered to rout the remaining soldiers, donning armor and riding on horseback with 200 men. When Ishida was reinforced by Sanada Masayuki, Sanada Yukimura and Asano Nagamasa, she was said to have slain the Sanada retainer, Miyage Takashige, in battle, taking his head as her trophy. Her accomplishments gave a huge boost to Narita army morale and forced Mitsunari to retreat, reporting his failure to Hideyoshi. Mitsunari has been ridiculed among warlord, to this day, the long strait where the Oshi incident occurred is also known as the "Ishida Tsutsumi". The Oshi castle was defended with a small number of soldiers and peasants, only fell when Hojo Ujimasa was defeated in Odawara. When Odawara Castle surrendered, Kaihime's father also chose to do the same with the hope of ending warfare. She and her father were put under Gamō Ujisato's care for a time. Sometime when her father was away, an internal rebellion was caused by Hamada Shugen and his younger brother. During this time, Kai's mother-in-law was killed. As soon as she heard about the incident, Kai brandished a sword and sought to end the rebels. She slew the instigator and two followers, effectively repressing the bloodshed. Hideyoshi heard of her bravery and married her. As a result, her father became one of Hideyoshi's trusted generals. He was rewarded with Karasuyama Castle and 20,000 koku. Much later, near the end of the Siege of Osaka's Summer Campaign, she is said to have fled with Toyotomi Hideyori's concubine and Hideyori's daughter. It is said that Kaihime personally defended Nāhime from Tokugawa force, and three of them became nuns at Tōkei-ji.
Kaihime appears in Koei's video gameSamurai Warriors 3 and Samurai Warriors 4, where her weapon is a sword-whip, and in the video game Takeda 3, as a general named Narita Kaihime.
She also appears as a character in Irem's trading card video game Sengoku Efuda-yugi: Hotogisu Ran.