School life
Many people will instantly recognize this kind of imagery. The life they lead in school is complex in the same ways that regular life is complex. They deal with life as it comes while also worrying about classes and grades, romance, friendship dynamics, and the ominous threat of existential crisis that faces all school graduates. This backdrop is imagery that provides a stark contrast for the action of the plot.
Lola's secret imagery
The imagery of Lola's private life is offered to the reader as a manifestation of her internal thought life which is highly disturbed. She struggles with intense suffering that leads her to eventually commit suicide, but not before she subjects herself to the painful life of repeated sexual assault on the bus, along with random anonymous sex with men who treat her like an object, and the random trips into dangerous parts of town alone at night—these are all painful reminders that her perception of reality is darkened by suffering.
Paranoia through imagery
The imagery that best describes the continual paranoia of the characters is the authority figures who scrutinize them, threatening them, invading their privacy and searching for reasons to harm them. These figures include the school authorities who are suspicious of their private lives, and the Communists who are concerned with their party after Lola's strange decision to join before her suicide, and the regular government who worries they are like their Nazi parents.
Evil and malice
The imagery of human evil is strong throughout the book. There are rapists and misogynists who abuse Lola, and there is the ominous underground of their city. Throughout the story, the government officials persecute the children though they are innocent, and when they graduate, they start appearing dead. The deaths are somewhat suspicious, because there was no reason to suspect that Georg for instance might kill himself, but there were plenty who might have killed him. They are chronically mistreated. Their parents are Nazis, which also contributes to this imagery.