"Forbidden Scrollery" is a manga series set in the fictional world of Gensokyo, a land where humans and supernatural beings coexist. The story revolves around Kosuzu Motoori, a young human girl who runs a bookstore specializing in rare and ancient texts. Kosuzu's life takes a dramatic turn when she discovers a mysterious book that grants her the ability to communicate with youkai, the supernatural creatures of Gensokyo. This newfound ability draws her into a series of supernatural incidents and conflicts, often involving the balance between humans and youkai.

The narrative frequently intersects with the broader Gensokyo setting, featuring recurring characters from the "Touhou Project" universe, such as Reimu Hakurei, the shrine maiden tasked with maintaining order, and Marisa Kirisame, a witch who often assists in resolving supernatural disturbances. These characters play significant roles in helping Kosuzu navigate the dangers posed by the youkai and the magical books she encounters. The series explores themes of curiosity, the consequences of meddling with the unknown, and the delicate equilibrium between the human and supernatural realms.

Kosuzu's interactions with the youkai and her growing understanding of their world form the core of the story. Her naivety and enthusiasm often lead her into perilous situations, but her resourcefulness and the aid of her allies help her overcome these challenges. The manga delves into the lore of Gensokyo, providing insights into the customs, hierarchies, and conflicts within the youkai community. Each chapter typically presents a self-contained incident or mystery, contributing to an overarching narrative that examines the interplay between humans and the supernatural.

The series maintains a balance between lighthearted moments and darker, more suspenseful elements, reflecting the duality of Gensokyo itself. Kosuzu's journey is marked by her evolving relationships with both humans and youkai, as well as her growing awareness of the responsibilities that come with her unique abilities. "Forbidden Scrollery" offers a detailed exploration of Gensokyo's rich mythology, making it a compelling read for fans of the "Touhou Project" and those interested in supernatural folklore.