The hero of the game, a high-school student named Touma, has a strange dream, in which he is a hero, a savior of the world in a parallel dimension. And now he is dying, having sacrificed his life for a beautiful woman whom he calls Ruby. Touma wakes up, unable to understand anything, and suddenly realizes it was not a dream... at least not entirely. A magical symbol is engraved on his forehead. Touma realizes that he will have to learn more about his heroic destiny. Meanwhile, a young, seductive English teacher arrives at his school...

[from MobyGames]