The supermarket is an important building in any city, for they provide a convenient way to purchase a variety of food in a family-friendly, safe environment. However, these stores changes in the blink of an eye once the unsold bento boxes go on their nightly half-off sales! War breaks out and friends become foes as each person fights for honor, pride, and dinner. There are no longer any people in these supermarkets, only Wolves and Dogs⁠—winners and losers. High schooler You Satou is painfully introduced to these battles after unknowingly stumbling into the war zone, but instead of choosing to avoid these nightly fights, he wants to join in. After seeing Satou's lack of fighting skills, upperclassman and Wolf Sen Yarizui invites him and Hana Oshiroi, a girl who enjoys spectating the brawls, to join her Half-Priced Food Lovers Club to show them the distinction between the Dogs and the Wolves. Together, they learn what it truly means to fight for your food.

Mahiro Yasaka is just an ordinary high school student, until one day he is suddenly attacked by a dangerous monster. Just when everything seems to be lost, he is saved by a silver-haired girl named Nyaruko, who claims to be the shape-shifting deity Nyarlathotep from horror author H. P. Lovecraft's Cthulhu Mythos, sent by the Space Defense Agency to Earth. She explains to Mahiro that the creature chasing him was an alien called Nightgaunt, who had planned on abducting and selling him as a slave. After rescuing him from the alien, the Lovecraftian deity falls madly in love with Mahiro and forces herself into his household, much to his chagrin. Moreover, they are soon joined by two others from the fictional universe: Cthuko, a girl obsessed with Nyaruko, and Hasuta, a young boy easily mistaken for a beautiful female. Together, the three eccentric aliens protect Mahiro from the various extraterrestrial dangers that threaten both his and Earth's well-being, all the while making his life a living hell.