Shin-chan gets his parents turned into kids and has to drag an alien around Japan hidden in his ass, which is exactly the kind of premise only this show could make work without a single moment of self-awareness. The comedy isn't trying to be clever about the absurdity; it commits completely. By the time you're forty minutes in, you've accepted that this is happening and you're laughing at the logistics of it, not the joke setup itself.

An alien called Shiriri arrives and turns Hiroshi and Misae into children. To get them back to normal, Shinnosuke has to make his way from one end of Japan to the other, with Shiriri hidden in his butt. While the boy is on the road, Shiriri's father is pushing ahead with an enormous conspiracy of his own. The result is a comedy film built on an outrageous road-trip premise.