Sinopsis
Gakurou Yajima has been able to see genyou, a kind of youkai that nobody else notices, since he was a child. He's learned to live with it. Then he starts high school, and the school turns out to have a room that no one knows about.
Someone has been living in it. She's a genyou named Nue, a girl who loves video games and has spent years sitting in that room waiting for a person to find it. Gakurou does, and the two of them meet.
From there the story follows Gakurou and Nue around the school grounds as he takes his first steps as a modern-day onmyouji.