Content Warning: This section of the guide references suicidal ideation and child sexual abuse, which feature in the source text.

Natsu Natsume is the novel’s protagonist. The novel spans a decade of her life, from 30 to her early 40s. Natsu is a single, childless, and asexual woman who works a minimum-wage job. In Breasts, Natsu grapples with her failure to fulfill the traditional expectations of womanhood prescribed by Japanese society. She suffers from loneliness, anxiety, and feelings of alienation, exacerbated by her grief at the premature deaths of her mother and grandmother, Komi. Natsu experiences intense dreams and hallucinatory interludes in which the past converges on the present.

In Eggs, Natsu has achieved material success but still feels unfulfilled. She decides that she wants to have a child, which puts her at odds with a society that discourages single motherhood. Natsu questions the validity of her wish because she has no desire to have sex or get married. As she looks into artificial insemination, she encounters the philosophy of anti-natalism, which forces her to consider whether she or anyone has a right to children. Along the way, Natsu falls in love with Jun Aizawa, but her desire for a relationship is complicated by her own perception of self.