Ōba Yōzō serves as the protagonist in the "No Longer Human" anime adaptation. Born into a wealthy political family as the son of a prominent congressman, he develops paralyzing dread of his father during childhood. This fear, coupled with early sexual abuse by household servants, instills deep alienation and distrust toward humanity. From youth, he perceives humans as incomprehensible and adopts a mask of buffoonery to conceal his terror and blend in, convinced this performance is necessary for acceptance. His constant fear of being exposed as an "imposter" defines his early existence.

During school years, classmate Takeichi sees through Yōzō's cheerful facade. Though terrified by this revelation, Yōzō befriends Takeichi to prevent exposure. Inspired by a Van Gogh painting Takeichi shows him, Yōzō begins expressing his inner torment through art. His self-portraits reveal grotesque, monstrous imagery mirroring his self-perception as fundamentally inhuman. Later, at university in Tokyo, he encounters Horiki, whose influence accelerates his plunge into alcoholism, prostitution, and fleeting communist group involvement. This culminates in a double-suicide pact with a married woman, Tsuneko; she dies while he survives, deepening his guilt and self-loathing. Flashbacks throughout his adulthood persistently revisit these formative traumas.

As an adult, Yōzō's relationships unravel further. After leaving university, he briefly lives with a single mother and her daughter, attempting a semblance of family life, but relapses into alcoholism and abandons them. He later forms a stabilizing bond with Yoshiko, whose innocence temporarily halts his self-destruction. He becomes a cartoonist and achieves sobriety, but Horiki's reappearance triggers another downward spiral. A pivotal moment occurs when Yoshiko is sexually assaulted in their home; Yōzō passively observes, paralyzed by traumatic memories of human cruelty and his own perceived inadequacy. This severs his last emotional connection, leading to morphine addiction and confinement in a mental institution. After release, he lives in rural isolation under his brother's guardianship, concluding he feels neither happiness nor unhappiness—only profound emptiness.

His psychological torment manifests visually through recurring symbols: Tsuneko's ghost haunting him, a demonic mask from childhood symbolizing societal pressure, and monstrous apparitions embodying his conviction of inherent inhumanity. These manifestations intensify during mental health crises, externalizing his internal struggles with guilt, paranoia, and dissociation. His art consistently depicts distorted, nightmarish figures, reinforcing his self-identity as a "failed human" disqualified from genuine connection.