Gin no Valkyries 

Ruka always dreamt of a silver knight calling her name while she's sleeping. And she never had boyfriend for all 17 years of her life because of her shyness. One day, there's a rumor about a stone that could make its owner having a sweet dream while sleeping. Followed by a strange event, Ruka tried the stone, and brought to the dream. But, what she found in her dream wasn't something that she's expected. And she woke up neither in her bed nor in her world. But in a world where Valkyries rule...