"Keshikasu-kun" centers on a young boy named Keshikasu, who lives in a small, rural village surrounded by dense forests and mysterious folklore. The village is known for its peculiar tradition of honoring spirits believed to inhabit the natural world, and Keshikasu is chosen as the next "Spirit Guardian," a role passed down through generations. As the Spirit Guardian, Keshikasu must maintain the balance between the human world and the spirit realm, ensuring harmony and preventing malevolent entities from causing chaos.

The narrative begins with Keshikasu reluctantly accepting his role after the sudden disappearance of his predecessor, an elderly woman revered by the villagers. Equipped with a sacred talisman and guided by a mischievous but loyal fox spirit named Akari, Keshikasu embarks on a journey to understand his responsibilities. Along the way, he encounters various spirits, both benevolent and hostile, each tied to the natural elements of the forest, rivers, and mountains. These interactions reveal the complexities of the spirit world and the consequences of human actions on the environment.

As Keshikasu grows into his role, he uncovers a deeper conflict involving a powerful, vengeful spirit seeking to disrupt the balance between worlds. This spirit, once a protector of the forest, was corrupted by human greed and deforestation, leading to its transformation into a destructive force. Keshikasu must confront this entity while grappling with his own doubts and fears, learning to harness his innate abilities and the wisdom passed down by his ancestors.

The series explores themes of environmental stewardship, the interconnectedness of life, and the weight of tradition. Supporting characters, such as Keshikasu's childhood friend Yuna and the village elder, provide insight into the cultural and spiritual significance of the Spirit Guardian role. The story balances episodic encounters with spirits and a larger, overarching plot, culminating in a climactic battle that tests Keshikasu's resolve and understanding of his purpose. Through his journey, Keshikasu not only protects his village but also bridges the gap between humans and spirits, fostering a renewed respect for the natural world.