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.

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.