Himari is a cheerful high school girl who has a childhood friend named Kou. As they grew older, Kou became colder and before she knew it, they have grown distant from each other. One day, Himari saw Kou in front of a torii gate and when she went after him through the torii entrance, she found herself in another world instead! She soon got into trouble but was saved thanks to the usually unfriendly and cold Kou putting his life on the line for her. "I promise to protect you." Will Himari be able to get back to her own world? And just what is the secret that Kou is keeping from her?