Hoshi no Furu Toki

When the protagonist Hasekura Akane was 10 years old she was given a sparkling jewel fragment by a mysterious beautiful woman. But in the blink of an eye, that women and the jewel both disappeared and thinking it was a dream Akane forgot all about it. And 7 years passed. Akane is now 17 years old and a second year in high school. Whenever thoughts of a boy make her heart flutter that sparkling jewel fragment appears in the palm of her hand. And along with that she feels a strange presence watching her. The cause is the owner of a dark gem that is opposed to the sparkling gem fragment that Akane has. Apparently in two weeks a comet will pass by and the dark gem will unleash it's power and cover the world in darkness. Various mysterious men appear around Akane because of the two gems. Will she fall in love or get betrayed? Will Akane be able to defend the world from the power of darkness? [Translated from the official site]

When the protagonist Hasekura Akane was 10 years old she was given a sparkling jewel fragment by a mysterious beautiful woman. But in the blink of an eye, that women and the jewel both disappeared and thinking it was a dream Akane forgot all about it. And 7 years passed. Akane is now 17 years old and a second year in high school. Whenever thoughts of a boy make her heart flutter that sparkling jewel fragment appears in the palm of her hand. And along with that she feels a strange presence watching her. The cause is the owner of a dark gem that is opposed to the sparkling gem fragment that Akane has. Apparently in two weeks a comet will pass by and the dark gem will unleash it's power and cover the world in darkness. Various mysterious men appear around Akane because of the two gems. Will she fall in love or get betrayed? Will Akane be able to defend the world from the power of darkness?