Three middle school boys, Kazuki, Toi, and Enta, accidentally break a statue of a mythical kappa in the Asakusa district of Tokyo. As punishment, Keppi, the mysterious prince of the Kappa Kingdom, appears and transforms them into kappa themselves. To earn the right to return to their human forms, the boys are given a task: they must hunt down and defeat the Kapa-zombies, grotesque creatures born from the twisted desires of humans. Their only weapon is the Sarazanmai, a special sound that can only be produced when the three of them are fully united in purpose. However, using this power comes at a great personal cost. Each time they perform the Sarazanmai and extract a zombie's shirikodama, one of their own deepest secrets or hidden desires is forcibly revealed to the other two. The narrative thus forces these three disconnected boys, each struggling with their own personal lies and unspoken feelings for people they care about, to confront what it truly means to form a genuine bond.

Sarazanmai: The Official Manga Anthology is a collection of over a dozen new short stories and illustrations set within this surreal and emotional world. Rather than a single continuous narrative, the book offers a series of vignettes that explore the characters and themes of the original anime from a variety of creative perspectives. The anthology features contributions from an extensive roster of manga artists, including several past collaborators of series creator Kunihiko Ikuhara. Among these are Chiho Saito, known for Revolutionary Girl Utena, Isuzu Shibata from Mawaru Penguindrum, and Lily Hoshino and Akiko Morishima from Yuri Kuma Arashi. The collection also includes work from the artist Misaki Saitoh, who drew the official spin-off manga, Sarazanmai: Reo and Mabu.

In addition to these returning creators, the anthology presents stories by a wide range of other artists such as Sakuya Amano, Akira Kasukabe, Chinatsu Kurahana, Asumiko Nakamura, pako, Akari Funato, and Kotetsuko Yamamoto. The book opens with cover art and a story by Migi, the original character designer for the anime. Through these varied artistic lenses, the anthology revisits the main trio of Kazuki, Toi, and Enta, as well as the mysterious police officers Reo Niiboshi and Mabu Akutsu, who play a key role in the original conflict between the Kappa Kingdom and the Otter Empire. The stories delve into the mundane and magical moments of the boys' lives, providing new glimpses into their relationships, their secret struggles, and the absurd yet heartfelt reality of fighting monsters while being forced to expose their own hearts.