What would you think if your best friend went on a date with the King of the Dark World – because she thought he was cute?! You’d think she’d been duped – and you’d be right. The fiendish King Rogles stands poised to conquer the other worlds of the universe: the Dream World of Queen Valia, and the Human World. Rogles and his five Dark Lords have taken the force of Yang from Queen Valia and sealed it into a Fantasm Jewel. Only a warrior with a heart perfectly balanced between Yin and Yang can wield the Sword of Valis against the encroaching darkness!
Yuko, a young student from the Human World, is the chosen one – and you will control her. She is to become the greatest warrior in the universe, never suspecting that her most fearsome battle will not be against a Dark Lord, but against her closest friend from the Human World – the one she warned, “Don’t go out with him, he’s the Dark…” But before she could finish, her friend ran off into The Darkness.
Yuuko Asou starts another school day as normal. When school ends, it suddenly starts to rain, so Yuuko tries to find refuge. In doing so, she encounters a fellow student, Reiko Kirishima, who talks with her and leaves her with many unanswered questions. Immediately afterward, Yuuko is attacked by a monster but a sword appears which she uses to protect herself. She tries to run home only to see that the entire city is being attacked by monsters.
After defeating them, Queen Valia appears in front of Yuuko telling her that the sword named Valis summoned her to save the dream world, Vecanti, from the claws of the evil emperor Rogles, so she can also save the human world. After being convinced by Valia, Yuuko starts to beat Rogles's generals one by one and get the phantasm jewels they carry, winning new powers.
After beating them, Yuuko goes to Rogles's domains and arrives at his castle only to find that Reiko, who is under under Rogles's control, is guarding the entrance because of her dark emotions. Yuuko fights her and makes her regain consciousness but then Reiko agonizes. Before her death, Reiko tells Yuuko about her bad emotions and her hard life, believing that nobody cared about her, but Yuuko then says her that she truly cares for her and they become friends. Shortly after, Reiko dies in her hands. Then Rogles appears and challenges Yuuko to enter his castle and fight him. Yuuko does so and kills him, enraged by the death of her friend. After this, Yuuko goes home with the presentiment that she will return to Vecanti someday.