はかれなはーと～誰がために君はある？～

Yukari is a high school student. One day, a boy appears in front of her when she is on her way home from school. He says, "Give me back the precious stone you stole." She doesn't know what he is talking about. He suddenly holds her tight and says, "Give me your life." She tries to escape from him, and she is scooped by another man who rides a horse astride. He says to her, "Give me back!" She is totally confused, and cries out loud in panic, "What are you doing? I don't have the precious stone!" Since then, her life is changed. There are other men who try to get back the precious stone from her. What will happen to Yukari? What is the precious stone?