"Hyakka Zukan" is a historical fantasy anime set in an alternate version of Japan during the Edo period, where supernatural beings known as "Ayaori" coexist with humans. The Ayaori are spirits that possess unique abilities and are bound to serve the shogunate. The story centers around the Hyakka, a special police force tasked with maintaining order between humans and Ayaori, ensuring that the latter do not misuse their powers.

The protagonist, Matsuri Kazuraba, is a young woman who becomes entangled with the Hyakka after encountering an Ayaori named Muramasa. Muramasa is a powerful and enigmatic spirit who wields a cursed sword capable of immense destruction. Matsuri, despite being human, forms a bond with Muramasa and joins the Hyakka to protect the balance between the two worlds. Her journey is marked by her struggle to understand the complexities of the Ayaori and her own role in the conflict.

The Hyakka is composed of various members, each with distinct personalities and abilities. Among them is Kiyomasa Senji, a skilled swordsman and one of the group's leaders, who harbors a deep mistrust of the Ayaori. Another key figure is Yagyu Jubei, a calm and collected strategist who often serves as the voice of reason within the group. The dynamics between the Hyakka members and their interactions with the Ayaori drive much of the narrative, exploring themes of loyalty, duty, and the blurred lines between good and evil.

The plot unfolds as the Hyakka investigates a series of disturbances caused by rogue Ayaori, uncovering a larger conspiracy that threatens the fragile peace between humans and spirits. As Matsuri delves deeper into the mysteries surrounding the Ayaori, she discovers secrets about her own past and the true nature of Muramasa's curse. The story builds toward a climactic confrontation that challenges the characters' beliefs and forces them to confront the consequences of their actions.

"Hyakka Zukan" blends action, intrigue, and supernatural elements, creating a narrative that explores the tensions between tradition and change, as well as the coexistence of different worlds. The series is characterized by its intricate plot, well-developed characters, and a richly imagined historical setting infused with fantasy.