Mizuo is a central figure in the story At a Confessional, the sixteenth episode of the anime Thus Spoke Kishibe Rohan. He is first encountered as a masked Japanese man who, while in Venice, enters a church confessional booth believing the occupant to be a priest. He is actually speaking to the manga artist Rohan Kishibe. Mizuo recounts a harrowing event from twenty-five years earlier when he was a young laborer in Venice. At that time, a starving homeless man begged him for food. Instead of helping, Mizuo cruelly forced the man to carry heavy bags of corn, an ordeal that led directly to the man's death. As the man lay dying, he placed a curse on Mizuo, vowing to reappear and bring him the greatest possible despair at the moment of his highest happiness.

After this incident, Mizuo's life became inexplicably charmed. He accumulated immense wealth, became famous, married a supermodel, and had a beloved daughter named Maria. However, this fortune was the direct result of the curse. Haunted by the knowledge of the beggar's threat, Mizuo spent years desperately trying to avoid true happiness, knowing it would trigger the curse's fulfillment. His primary motivation became a struggle to protect his family and himself from a supernatural retribution he felt powerless to stop.

The curse manifested when Mizuo finally felt genuine happiness while watching his daughter play. At that moment, the spirit of the beggar took possession of Maria. The spirit offered Mizuo a single chance to break the curse: he had to throw a piece of popcorn high into the air and catch it in his mouth three times in a row. On the first two attempts, Mizuo succeeded, but he was thwarted on the third by a flock of pigeons. Failing the challenge, the spirit immediately decapitated him.

Mizuo's story does not end there. Despite losing his head, he survived and, with the help of his loyal servant, dragged himself into the church where Rohan was sitting, still alive and still speaking. In this state, he continued his confession, revealing the full depth of his terror and desperation. His key relationship is with the vengeful spirit of the homeless man, which defines his entire adult life. His relationship with his daughter Maria is also central, as she becomes the vessel for the spirit and the instrument of his doom.

In terms of abilities, Mizuo does not possess supernatural powers. His notable trait is his extreme resilience and cunning. He survived for years under a supernatural curse by actively avoiding joy, and he survived being beheaded through sheer willpower and the aid of his servant. He is depicted as a man burdened by guilt and fear, whose attempt to escape his past actions only led to a more ironic and terrible fate. His role in the story is to serve as the confessor, providing the central narrative of a curse that Rohan investigates. Mizuo is both the protagonist of the tragic tale he tells and, in later live-action adaptations, is reconceived as a primary antagonist, highlighting the complexity and duality of his character as both a victim and a perpetrator.