Hoshi no Furu Toki

When Hasekura Akane was ten, a mysterious beautiful woman pressed a glowing jewel fragment into her hand — then vanished, along with the jewel, in an instant. Akane decided she had imagined it. Seven years passed. Now seventeen and in her second year of high school, Akane notices something strange: whenever a boy makes her heart flutter, the jewel fragment materializes in her palm. She also senses that someone is watching her. A dark gem opposed to hers exists somewhere close, and a comet two weeks away will amplify its power and plunge the world into darkness if nothing is done. Strange men begin appearing around Akane, drawn by the two gems — and by the question of whether she will use hers in time.