The final installment of the Sea of Fertility tetralogy centers on the aging Shigekuni Honda as he encounters a young man he believes to be the latest reincarnation of his long-lost friend.

Honda, now an elderly lawyer, adopts Toru Yasunaga, a youth who exhibits signs of being the fourth incarnation of Kiyoaki Matsugae. As Honda attempts to mentor the boy, he faces the cold, nihilistic defiance of a protagonist who rejects the world and its moral structures. The narrative framework shifts between Honda's obsessive search for spiritual continuity and the harsh reality of Toru's destructive nature, leading to a confrontation that challenges the validity of the entire reincarnation cycle. The prose maintains a detached, analytical tone, reflecting the protagonist's own intellectual isolation.

Discussion often centers on the bleak, uncompromising conclusion of the tetralogy and how it serves as a final statement on the author's own life and philosophy. Readers frequently highlight the stark contrast between the romanticism of the earlier volumes and the cold, clinical detachment found in this final entry. Critics often note the technical precision of the prose, which mirrors the protagonist's own rigid and increasingly isolated worldview. The work is widely regarded as a meditation on the futility of seeking meaning in a world defined by impermanence and decay. Many readers find the shift in tone to be a challenging but necessary resolution to the complex themes established throughout the series.