"Haunted Bookstore - Gateway to a Parallel Universe" centers around Kaori, a young woman who inherits a mysterious bookstore from her late grandfather. The bookstore, located in a secluded area, serves as a gateway between the human world and a parallel universe inhabited by spirits, yokai, and other supernatural entities. Kaori, initially unaware of the store's true nature, discovers that her grandfather was a mediator between these two realms, ensuring balance and resolving conflicts. As she takes over the bookstore, she becomes entangled in the affairs of both worlds, guided by her grandfather's spirit and a cast of supernatural beings who frequent the shop.

The narrative unfolds through episodic encounters with various spirits and yokai, each bringing their own stories, struggles, and requests for help. Kaori, with her growing understanding of the supernatural, assists these entities while navigating her own challenges as a human in a world filled with magic and danger. Key characters include Shiba, a fox spirit who serves as her protector and guide; Taro, a mischievous but loyal tanuki; and a host of other spirits who form a community around the bookstore. The series explores themes of coexistence, responsibility, and the blurred boundaries between the human and supernatural realms, all while maintaining a balance of mystery, humor, and emotional depth. The bookstore itself acts as a central hub, symbolizing the connection between worlds and the legacy Kaori must uphold.