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

A salaryman named Sanematsu takes care of his six siblings, the Matsuno brothers become girls and argue, and a fight between Choromatsu and Osomatsu occurs.

Jyushimatsu goes to a job interview, proving to be a total nuisance for the interviewers. Chibita is asked out on a date by the fairy of a flower he saved.

In an apocalyptic world, the Idol Matsunos battle against Iyami and Dekapan, who are robbing the dry-skinned citizens of all of their lotion. Ichimatsu is forced to pretend to be Karamatsu after Osomatsu catches him wearing his clothes.

Jyushimatsu carries out incredible feats. Meanwhile, the other brothers try to find out when Jyushimatsu developed his odd personality.

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.