Valkyries—legendary female warriors from Asgard, the realm of the gods—are dispatched by Odin to defend Earth against the escalating threat of demons. To counter these dangers, nine valkyries, disguised as the Saotome sisters, must increase their power by engaging in various romantic activities with their designated lover, Einherjar. Meanwhile, the socially anxious Takuma Akutsu discovers that Odin has selected him to be the valkyries' lover. Despite his sheer terror, he consents to let the sisters reside in his large but vacant home to assist them in their war against demons. With nine beautiful women living under his roof, will Takuma succeed in overcoming his fear of society and become someone worthy of saving the world?