There are two worlds in this world: the human world and the magical world. Sumi, the main character who attends the magic academy in the human world, spends her days hiding in a corner away from people because of a certain behavior that she does reflexively. She is called the "charcoal" girl. She really wants to be friends with everyone, but...Sumi has a turning point! Gita, an emissary from the demon world, beckons her to become the Demon King! I've always been in the corner, and I'm not used to being in front of people. I'm not used to being in the public eye, and I'm a human, but a Demon King who rules over the demon tribe...! Sumi is worried that she won't be able to handle it, but her follower, Gita, is always full of confidence and assures her that everything will be fine...