The holy sword Excalibur is a mystical blade said to grant its wielder any desire. Upon learning of its existence, the female ninja Seiryu plots to seize the sword and use it to dominate the world. Meanwhile, her younger sister Suzaku resolves to stop her sister's ambitions and set her on the right path by claiming Excalibur herself. However, Seiryu harbors twisted affection for Suzaku, and upon discovering her actions, subjects her to lewd torture. Enduring the torment, Suzaku escapes and enters the game "Holy Sword Story," where Excalibur is rumored to be hidden. Seeking the legendary sword within the game world, Suzaku advances alongside allies including the vampire Reymia, the sorcerer Bordau, the beastwoman Mazu, and the dark ninja Hanza. But Seiryu also invades the game world, relentlessly pursuing her sister. Can Suzaku obtain Excalibur and finally stop Seiryu's dark ambitions? The story unfolds to reveal the answer.