Sayuri Maedagawa, a normal high school girl with normal high school problems, finds her world turned upside down when her supposed grandmother reveals everything she knows is wrong: magic is real, demons exist, her grandmother is actually her 1,000 year old sister, and Sayuri and her hated rival Ryuichi are reincarnated lovers who must save the world.

Ryuichi doesn't buy the story, leaving Sayuri to discover the truth for herself.

Sayuri meets Suiren, the water goddess. Suiren reveals Sayuri's past as a priestess and how she came about her powers. Suiren gives her an ancient weapon, a staff, that Sayuri wielded a thousand years ago as a priestess. But before she can absorb what she's learned, Sayuri is attacked by the demon Chiro, sent by his master to retrieve the weapon. Suiren saves Sayuri, but because she's connected to water she cannot help Sayuri unless water is nearby. Sayuri realizes she will have to learn the weapon as well as convince Ryuichi that what Hashimoto said was true... easier said that done.

Hashimoto forces Ryuichi to help them by working out a deal with the principal of his school to curb his "attitude." His willingness to peacefully work with Sayuri is hindered, however, when he discovers she starts dating his best friend Daisuke. Their first mission is to retrieve the ancient sword Ryuichi used in his previous life over a thousand years ago. It is during this search they meet Makku, a half human / half cat hybrid entrusted by Suiren to guard the weapon. However, having been stolen long ago, they must use magic to find its new location.

Unfortunately for them Chiro is doing the same thing, and eventually the opposing sides meet at the cave the sword is hidden at. Ryuichi, having grabbed the sword while Sayuri and Makku act as a distraction, kills Chiro. Having only just slain their enemy, the three encounter a young girl, Kikyo, who thanks them for disposing of her competition and promises to see them soon.

Sayuri up to this point was successful keeping her school and secret lives separate, but that is all changed when she has to deal not only with a serious fight with her best friend Mai, but the dangerous Kikyo posing as a student. Since Chiro failed to steal the weapons, the Demon Lord's new goal is to retrieve a magical item only the heroes possess. Unfortunately for them they have no idea what it is. Kikyo is convinced they have it, though, and having already taken the hunt to their school, challenges Sayuri and Ryuichi to meet her at the school theater, promising to kill innocent people if they fail to show. Their hand forced, the two walk into an obvious trap. They manage to escape, however, thanks to a timely distraction by Makku. Events take a surprising turn for Kikyo when rubble from a building traps her and she is saved by the very people she attempted to kill mere minutes before.

Confused, Kikyo runs off, leaving the heroes baffled at her odd behavior.

With Kikyo now missing Jao, the demon who trained her, takes up the hunt for the magical item, researching every book he can. In the meantime Sayuri learns a bit about Ryuichi's home life and attempts to connect with him, only to meet rejection. Their conversation is cut short, however, as Jao appears with his new found knowledge of the magical item's location. After easily defeating Ryuichi Jao rips a jewel from Sayuri's chest, leaving behind a shadow of the girl she was moments before. Makku makes a timely appearance, though, stealing the jewel and helping the two escape.

When they return to the magic shop Hashimoto, after learning the situation, explains the magical jewel had been grafted to Sayuri's soul to hide it from the enemy. Sayuri's reaction to it's removal is because her body became accustomed to it, but since it was never actually a part of her soul to begin with it can't be returned... not with Hashimoto's level of magic, anyway. Sayuri will recover, but only in time.