TV-Series
Description
Medama Oyaji originated as an adult member of the Ghost Tribe afflicted by an incurable "melting disease." During his illness, he secluded himself with his pregnant wife Iwako, selling his blood for income. This blood caused transfusion recipients to resemble ghosts, drawing attention from authorities. Discovered by blood bank employee Mizuki, he negotiated a few months' respite before both he and Iwako succumbed to the illness prior to their child's birth. His spirit willed itself into his last living tissue—his eyeball—driven by paternal devotion after Kitarō was born posthumously from Iwako's grave. This event typically occurs in the early 1960s, though one live-action film places it in the Edo period.

His current form consists of a small body topped by a single giant eyeball head, usually unclothed. His pre-decay appearance varied: early media depicted him as a bandage-wrapped mummy due to his disease. The 2018 anime showed his pre-disease form as a gray-haired humanoid resembling Kitarō, covering one eye. Hakaba Kitarō retained the bandaged mummy appearance, reflecting differing interpretations.

Despite a fragile look, he exhibits extreme resilience, regenerating after being crushed, deep-fried, or flattened, and surviving without sustenance for up to ten years. He wields abilities like body manipulation, eyeball substitution, and possessing inanimate objects or living bodies. He possesses encyclopedic knowledge of global yōkai, occult phenomena, and their weaknesses, gained during extensive travels before Kitarō's birth. This knowledge aids his role as Kitarō's primary advisor. He maintains a personal relationship with Enma-Daiō, ruler of the afterlife, enabling direct access to hell for mediation or requests.

Character development varies across adaptations. Early anime emphasized anxious, doting parenthood, often scolding or weeping over Kitarō's safety. The third series introduced abilities like emitting beams to reveal hidden text and diverged by supporting Kitarō's romance with human Yumeko. Later portrayals typically show him cautioning against human-yōkai relationships due to lifespan disparities. The fifth series added comedic elements: bathing in diverse liquids (sake, cola), exercising, fearing fireworks, and enjoying television. The sixth series explored emotional complexity; temporarily regaining a youthful form, he expressed shame over his diminutive state, believing it forced Kitarō into premature maturity. Hakaba Kitarō presented a less sentimental version, displaying frustration toward Kitarō's irresponsibility and harshness toward allies like Nezumi-Otoko.

He frequently bathes in small containers like teacups, symbolizing fastidiousness. Though rarely seen eating initially, later adaptations show him consuming morning dew, cherries, plums, and fish-eye soup. He possesses a concealed mouth under his eyeball, revealed sparingly, and lacks teeth. Personal items include a silk hat from "English demons" and a shoe from Santa Claus. His personality balances calm rationality with deep loyalty, often prioritizing Kitarō's well-being above all else.

His relationships define his narrative function. Unwavering paternal love for Kitarō motivates his actions, from strategic guidance to emotional support. He intermittently mentors Neko-Musume, even suggesting her as a potential spouse for Kitarō before humorously retracting this after witnessing her temper. His dynamic with Nezumi-Otoko ranges from collaborative to antagonistic, particularly in Hakaba Kitarō where he openly mocks the character.