"Everyone has secrets. Including that girl."

To those who are unfamiliar of him, Kobayashi Tatsuya looks nothing more than an ordinary high school student living out his daily life nonchalantly.

But beneath that normality, he's actually a "Professional" in underground works.

Intel gathering, supplying illicit goods, unveiling secrets, you name it. He can do any illegal job, no matter how significant or trivial they are.

Until one day, fate led him to a disaster when he unintentionally witnessed Shinonome Hikari, the undecipherable Class Anomaly, floating in midair.

That girl has a secret.

And it's something that shouldn't exist in this world.

From there, an abnormal life of two species from different worlds begin.