Yozo Oba is the tortured author and unreliable narrator of the three notebooks that comprise the bulk of No Longer Human. His appearance is depicted in three photographs examined by an unnamed narrator in the Prologue. These three photographs correspond to his appearance in each of the three notebooks. As a child, Yozo is precocious by design—an impish child who uses his antics to hide his fear, shame, and inability to relate to humanity. These fundamental flaws carry over into young adulthood; in the second notebook, he is a handsome young man whose smiling photograph lacks humanity, betraying the depth of terror and isolation that his comical persona seeks to hide. In the third photograph and notebook, he is only 27, but his gray hair and forgettable appearance prevent him from being labeled an ordinary human being.

Yozo is the son of a politician, and he grew up in a wealthy household in the Japanese countryside along with his brothers, sisters, and cousins. He was raised around women, but this makes them even more terrifying to him than men. Yozo’s problems with women hound him throughout his life. This is compounded by the fact that women are easily attracted to him, and that he was likely sexually assaulted as a child by a maidservant in his house.