Record of the Demons of the Lower Realm

I'm an ordinary student. Near the end of my studies, I met a rather strange girl and realized that the world I lived in was far more complicated than it seemed. In this world, both familiar and strange, there are not only humans, but also countless monstrous beasts hidden among them. And they're not the only ones. Humans and demons coexist, forming different factions with tangled relationships and very different aims. As I learned more, I discovered that something seemed to be quietly brewing in this world, and that I might be a crucial part of it...