On the order of Toyotomi Hideyoshi, an army of 30,000 men led by Ishida Mitsunari came to Narita's castle "oshijyo". Mitsunari attacked oshijyo with a "water offensive". The raging waters attacked! Princess Kai, armed with armor and her famous sword "Nami-Kiri" in hand, goes into battle! The final battle of the Princess Kai, renowned as the "strongest princess general of the Sengoku", begins!

小田原城を本拠に関東一円を支配した戦国大名・北条氏を打倒すべく、豊臣秀吉が動き出した。 北条氏配下の勢力・成田氏の居城”忍城”に、石田三成率いる3万の軍勢が押し寄せる。 三成は”水攻め”をもって忍城を攻撃。激流が襲いかかる！ 甲斐姫は自ら鎧をまとい、名刀”浪切”を手に出陣！ ”戦国最強の姫武将”と名高い甲斐姫の最後の戦いが始まる！