Valkyries—legendary female warriors from the land of gods, Asgard—are sent by Odin to protect Earth against the growing threat of demons. To overcome these threats, nine valkyries under the guise of the Saotome sisters will have to level up by performing a variety of romantic acts with their official lover, Einherjar. Meanwhile, the socially anxious Takuma Akutsu learns that Odin has chosen him as the valkyries' lover. Despite his utter horror, however, he agrees to let the sisters stay in his big yet empty house to help them in their war against demons. With nine beautiful women sharing his roof, will Takuma manage to prevail over his fear of society and become someone worthy of saving the world? [Written by MAL Rewrite]

In response to the worsening crime rate, Japan creates Tokyo Butei High, an elite academy where "Butei" or armed detectives hone their deadly skills in hopes of becoming mercenary-like agents of justice. One particular Butei is Kinji Tooyama, an anti-social and curt sophomore dropout who was once a student of the combat-centric Assault Division. Kinji now lives a life of leisure studying logistics in order to cover up his powerful but embarrassing special ability. However, his peaceful days soon come to an end when he becomes the target of the infamous "Butei Killer," and runs into an emotional hurricane and outspoken prodigy of the highest rank, Aria Holmes Kanzaki, who saves Kinji's life and demands that he become her partner after seeing what he is truly capable of.