High schoolers Haruka and Hikage are best friends and have been living normal lives until Ruche, the daughter of a demon lord, comes to Earth to wreak havoc on humanity. Ruche's mission is to bring fear to humans and to take over the planet. However, as menacing as Ruche tries to be, her evil plots end up being nothing more than pranks at best. As Ruche enrolls in the same class as Haruka and Hikage, she comes up with diabolical plans such as diluting shampoo bottles only to find out that has no effect on anyone. Will Ruche be able to become as evil as she thinks she is?