Mizuki is a human man who becomes the adoptive father of Kitaro in the anime Hakaba Kitaro. He works as a salaryman, often depicted in a black suit, and leads a relatively ordinary life before his encounter with the supernatural. His background is that of an average working individual who stumbles into the world of yokai after being tasked by a blood bank to investigate mysterious blood donations. This investigation leads him to Kitaro’s parents, a yokai couple, and after their deaths, Mizuki reluctantly takes on the role of raising their infant son, who crawls out of his mother’s grave.

Mizuki’s personality is pragmatic and hardworking, but he is often overwhelmed by the bizarre circumstances surrounding his adopted son. He frequently shows frustration and a lack of gratitude from Kitaro, whose behavior is more mischievous and darkly humorous than affectionate. Despite this, Mizuki continues to provide for Kitaro, working hard to put food on the table even when his efforts go unappreciated. His motivation is not heroism but a sense of duty or obligation, and he often feels out of his depth in the chaotic, supernatural world he has been drawn into.

In the story, Mizuki serves as a human anchor and a contrast to the yokai characters. His role is primarily that of a caretaker and occasional comic relief, as his ordinary human reactions highlight the strangeness of Kitaro’s world. He also inadvertently causes a significant event: when he first meets Kitaro, he panics and pushes the baby, accidentally damaging one of his eyes, which becomes a permanent part of Kitaro’s appearance.

Mizuki’s key relationships include his strained but persistent bond with Kitaro, who never fully acknowledges his efforts, and his interactions with Medama Oyaji, Kitaro’s ghostly father who exists as a floating eyeball. Medama Oyaji often guides the situation, leaving Mizuki to deal with the practicalities. Mizuki also interacts with Nezumi Otoko, a manipulative rat-like yokai, and other supernatural beings, often to his own misfortune.

Development for Mizuki is subtle: he begins as an ordinary man thrust into an extraordinary situation and gradually accepts his role, though he never becomes a heroic figure. His growth is measured in his continued commitment to Kitaro despite the lack of reward. Mizuki has no notable supernatural abilities; his only strengths are his perseverance and his willingness to provide a home for a creature that is not fully human. His character underscores the theme of mundane human responsibility in the face of the inexplicable.