There are strange creatures in this world, and their appearances are ever-changing. They are called "youmu". Those who make it their business to eliminate youmu are called aliens. The protagonist of this work, Akito Kanhara (voiced by KENN), looks like an ordinary high school boy, but he is actually a "half-demon" born from the combination of a human and a youmu. He has an immortal body. One evening, he met a girl, Mirai Kuriyama (voiced by Risa Taneda), who wanted to jump off the building on the rooftop of the campus. Unexpectedly, the girl attacked him. It turned out that the beautiful girl with glasses who looked like an ordinary freshman was actually an alien who could manipulate blood. Mirai Kuriyama, who has special abilities, attracted the attention of the famous alien family, the Naze family. Naze Mitsuki (voiced by Minori Chihara), who is in the literary club with Akito, is the second daughter of the Naze family. She told Akito to stay away from Kuriyama. The rampant youmu, the alien who walks alone in the world, and the rare half-demon unfold a strange fantasy story on the other side of the boundary.