The Iyahaya family, one of Japan's most prominent conglomerates based in Iyahate Prefecture, has decided to take care of a relative named Nantomo while his parents are transferred overseas. Iyahaya Sayoko can't help but be curious about her relative's boy of the same age. What kind of boy is this eccentric Nantomo?

In the meantime, a boy in a tattered coat appears before Sayoko's eyes, a poorly dressed eccentric person who eats their dog's food. When she asked him what his name was, he said, "Iyahaya Nantomo (Oh no... Not at all...)", how unclear. Sayoko and her grandmother hurriedly invited him into their house, convinced that he was their relative, Nantomo.

Even though he is not Nantomo, the head of the Iyahaya family, Totetsumo, decides to keep the poor, mysterious boy as the Nantomo and sends him to Kenkin school, the same school as Sayoko.

The school is in the state of Cold War between the Hatesate family conglomerate and the Iyahaya family conglomerate. With the arrival of Nantomo, the school is dragged into a great explosion of madness.