Tsuki no Kage Kage no Umi

Yoko Nakajima is an ordinary Japanese high school student with red hair. Her routine changes when a young blond-haired boy named Keiki, who is actually a unicorn, claims she is his master and insists they return to his kingdom. After Keiki disappears, Yoko is left alone in an unfamiliar place, armed only with a magic sword and a magic stone. When Keiki reappears at her school, Yoko's life takes a dramatic turn. She faces challenges in a land she doesn't know, pursued by demons, as she seeks to survive and learn more about herself.