Shimezō is a young zipper yōkai from a lineage devoted to sealing open zippers as their honorable duty. Still in training, he has yet to successfully close any zipper, reflecting his inexperience with this inherited task. His development initiates upon meeting Hiroki, a human boy who lost 500 yen through an unzipped coin purse. The two bond over shared frustrations with their mothers' constant nagging, prompting them to flee home together toward Hiroki's grandfather's residence. Hiroki's sister, Chie, accompanies them on this journey, which serves as the central catalyst for Shimezō's experiences and growth.