"Nezumi no Yomeiri" is a historical fantasy anime set in feudal Japan, blending elements of folklore, romance, and supernatural intrigue. The narrative centers around a young woman named Sayo, who lives in a remote village plagued by mysterious disappearances. The villagers believe these incidents are tied to a local legend about a rat spirit demanding brides to maintain peace. When Sayo is chosen as the next sacrificial bride, she is taken to the spirit's lair, where she encounters a enigmatic figure named Shiro, who is neither fully human nor entirely spirit.

Shiro, the rat spirit, is bound by a curse that compels him to take brides, though he harbors no malice toward them. As Sayo spends time in his realm, she begins to uncover the truth behind the curse and the tragic history that binds Shiro to his fate. The story explores themes of duty, sacrifice, and the blurred lines between humanity and the supernatural. Sayo's determination to break the curse and free Shiro drives much of the plot, as she navigates the dangers of the spirit world and confronts the prejudices of her own village.

The series delves into the complexities of the characters' relationships, particularly the growing bond between Sayo and Shiro. Their interactions reveal layers of vulnerability and resilience, challenging the initial assumptions about their roles as victim and oppressor. Supporting characters, such as the village elders and other spirits, add depth to the narrative, highlighting the cultural and moral dilemmas surrounding the sacrifices.

The plot unfolds through a series of flashbacks and revelations, gradually piecing together the origins of the curse and the true nature of the rat spirit. The anime balances moments of tension and action with quieter, introspective scenes, creating a narrative that is both engaging and emotionally resonant. By the conclusion, the story resolves the central conflict while leaving room for reflection on the themes of redemption and the enduring power of human connection.