Shy eleven-year-old Japanese schoolgirl Cheko Komori receives a mysterious book as a birthday gift from her father. Opening it, she accidentally releases Tickle, a mischievous witch imprisoned inside for her pranks. Skeptical, Cheko demands proof of magic, prompting Tickle to instantly retrieve Cheko's scarf from her friend Miko – who had moved to Hokkaido but promised to attend the birthday. Convinced by this act, Cheko forms an immediate bond with Tickle.

To integrate Tickle into the household undetected, Tickle alters the family's memories, making them believe she is Cheko's twin sister. Cheko becomes Tickle's confidante and moral compass, frequently cautioning against irresponsible magic use, especially when pranks target Cheko's younger sister, Hina. Cheko wields the sealing incantation "Pekepon" to return Tickle to the book as punishment for excessive mischief, followed by "Kurunka Kurunkotekopokoten" to release her, reinforcing Cheko's role as a stabilizing force.

Throughout the series, Cheko evolves from timidity to assertiveness, exemplified when she confronts classmate Satomi Yano for bullying a junior student. Beyond Tickle, she maintains a close, sometimes strained relationship with Hina, who often disrupts their activities. Cheko also shows empathy towards classmates facing adversity, like Fuko enduring weight-related teasing. A subplot involves both Cheko and Tickle harboring a crush on schoolmate Saburo, adding youthful romantic tension.

The series concludes as Cheko witnesses Tickle using magic to stop a knife from injuring their mother, irrevocably exposing Tickle's true nature. Though Tickle prepares to return to the magic kingdom, Hina destroys the book, severing Tickle's connection to her homeland. Tickle remains with the family but loses her magic, an outcome Cheko accepts as it solidifies their familial bond, highlighting Cheko's centrality to Tickle's human experience and their shared journey.