Oba Yozo is the main character of this melancholy piece as he narrates his feelings of disconnect with society. Yozo consistently seeks meaning in his life and strives to fill his emptiness with various things. He writes of how often life's cruelties seem to appear to him.

I can’t even guess myself what it must be to live the life of a human being. I was born in a village in the Northeast, and it wasn’t until I was quite big that I saw my first train. I climbed up and down the station bridge... I was convinced that the bridge had been provided to lend an exotic touch and to make the station premises a place of pleasant diversity, like some foreign playground. I remained under this delusion for quite a long time... When I later discovered that the bridge was nothing more than a utilitarian device, I lost all interest in it.

While charming and likeable, Yozo struggles to sustain normal relationships, even with his family members (whom he feels he constantly disappoints). He does not feel that he can truly be human, and he tries to dull his pain through partying and prostitutes.

I never could think of prostitutes as human beings or even as women. They seemed more like imbeciles or lunatics. But in their arms I felt absolute security. I could sleep soundly. It was pathetic how utterly devoid of greed they really were. And perhaps because they felt for me something like an affinity for their kind, these prostitutes always showed me a natural friendliness which never became oppressive. Friendliness with no ulterior motive, friendliness stripped of high-pressure salesmanship, for someone who might never come again. Some nights I saw these imbecile, lunatic prostitutes with the halo of Mary.

Yozo's art reflects his struggles:

The pictures I drew were so heart-rending as to stupefy even myself. Here was the true self I had so desperately hidden. I had smiled cheerfully; I had made others laugh; but this was the harrowing reality. I secretly affirmed this self, was sure that there was no escape from it.

Many believe that Yozo represents the author of the book, Shuji Tsushima, as both struggled with despair and feelings of failure. Tsushima was born to a large, aristocratic family in Japan but struggled with depression for most of his life. He also had many failed relationships with women. In his alienation and attempts to understand life's complexities, Yozo states:

I am convinced that human life is filled with many pure, happy, serene examples of insincerity, truly splendid of their kind-of people deceiving one another without (strangely enough) any wounds being inflicted, of people who seem unaware even that they are deceiving one another.

There are some people whose dread of human beings is so morbid that they reach a point where they yearn to see with their own eyes monsters of ever more horrible shapes. And the more nervous they are —the quicker to take fright—the more violent they pray that every storm will be.

No Longer Human was the last book written by Tsushima before his death.