The Matsuno brothers compete to ensure their divorcing parents will care of each of them. Meanwhile, Totoko asks the brothers for help in a crisis.

The Matsunos are invited to Hatobou's birthday part. Meanwhile, Iyami discovers that his buckteeth contain a rare metal.

Wanting to become the main protagonist of the franchise again, Iyami holds a bizarre kart race to determine who the protagonist of Osomatsu-san will be.