Fire and Shade

A 17-year-old girl is suddenly taken to a magical world. There, she manages to slay a dragon, become a queen, get married, have children, and eventually pass away decades later... only to be woken up by the bell at her high school, young and in her private school uniform again, as if nothing happened. That is, until she notices that her wedding ring, from her lover in the magic realm, is still on her finger