A man is assaulted by someone with a bat and attempts to figure out why.

It is 1980. Sadatomo is at a secondary school in a small town. His parents barely take any notice of him. The strict teacher Kobayashi has hung up a 'humanity index' in the classroom, divided into the categories 'delinquents', 'scum' and 'people'. In each category he has hung name-cards of pupils. One day Kobayashi finds out that Sadatomo and his friends have stolen some things from a shop for fun. Their fathers are informed and as punishment, the children have to write a 'self-critical' essay of no less than thirty pages. For the first time, Sadatomo is beaten by his father. Shocked, he writes a piece entitled 'I am an onion', in which the teacher thinks he can detect a first sign of humanity. That is the start of a confusing situation in which it gets hard to distinguish lies, truth, justified self-criticism and opportunist wheeler dealing, even for the boys.