Shinnosuke Nohara takes center stage in "Eiga Crayon Shin-chan Shūrai! Uchūjin Shiriri." After an alien named Shiriri transforms his parents, Hiroshi and Misae, into children with a mysterious ray, Shinnosuke must find a way to restore them. The solution requires locating Shiriri's father somewhere in Japan. Shinnosuke journeys across the country with Shiriri hidden in his buttocks, adapting to the strange circumstances. What begins as a family predicament soon spreads to involve Shinnosuke's friends, eventually engulfing the entire nation. The narrative follows Shinnosuke's quest to reverse his parents' transformation and navigate the escalating crisis caused by Shiriri's father's alien conspiracy.