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.
When a bizarre alien named Shiriri crash-lands in Japan, Shin-chan's parents suddenly transform into children. Desperate to reverse the spell, Shin-chan discovers that Shiriri holds the key to restoring them, but there's a catch: the tiny alien needs to stay hidden inside his butt for the journey across the entire country. What should be a straightforward rescue mission spirals into comedic chaos as Shin-chan drags his new extraterrestrial companion from one end of Japan to the other, dealing with the usual mishaps and misadventures that plague the Nohara family. Meanwhile, Shiriri's father is executing a sinister plan that could threaten Earth itself. Caught between helping his accidentally-miniaturized parents and stopping an alien invasion, Shin-chan bumbles through his most ridiculous adventure yet. This film doubles down on the franchise's trademark absurdist humor, mixing crude jokes with surprisingly heartfelt family moments. It's pure Shin-chan chaos: outrageous premise, genuine stakes buried under layers of silliness, and characters who take the most insane situations completely seriously.