"Kunimitsu no Matsuri" centers on Kunimitsu, a high school student who becomes entangled in a mysterious and dangerous world after encountering a supernatural entity during a local festival. The story unfolds in a rural town where ancient traditions and rituals hold significant power, and the line between the human world and the spiritual realm is thin. Kunimitsu, initially an ordinary teenager, is thrust into a role he never anticipated when he inadvertently disrupts a sacred ritual, awakening a vengeful spirit tied to the town's history.

As the narrative progresses, Kunimitsu discovers that his actions have triggered a series of calamities, including the resurgence of malevolent spirits and the destabilization of the town's spiritual balance. To rectify his mistake, he must navigate a complex web of folklore, alliances, and rivalries among both human and supernatural factions. Key characters include Ayame, a shrine maiden with deep knowledge of the town's spiritual practices, and Sora, a enigmatic figure who oscillates between ally and antagonist, harboring secrets tied to the town's past.

The plot delves into themes of responsibility, tradition, and the consequences of meddling with forces beyond human understanding. Kunimitsu's journey is marked by his growth from a reluctant participant to an active protector of the town, as he learns to harness his latent abilities and confront the darker aspects of the spiritual world. The story balances moments of tension and action with quieter, introspective scenes that explore the characters' motivations and the town's rich cultural heritage. Through its blend of supernatural intrigue and character-driven drama, "Kunimitsu no Matsuri" offers a compelling exploration of the intersection between the mundane and the mystical.