Final answer:
Rahim Khan's secret in 'The Kite Runner' reveals to Amir that Hassan is his half-brother, profoundly affecting Amir's sense of guilt and prompting a journey of redemption.
Step-by-step explanation:
The question 'What did Rahim's secret reveal to Amir?' pertains to the novel 'The Kite Runner' by Khaled Hosseini. In the narrative, Rahim Khan's secret significantly alters the course of the protagonist, Amir's life. It is revealed that Hassan, who is Amir's loyal friend and the person he had previously wronged, is actually his half-brother.
This revelation comes as a shock to Amir and adds complexities to his feelings of guilt and his understanding of his family's past. The secret uncovers the true nature of the relationships between the characters and prompts Amir to seek redemption and atonement for his past actions.