Pelangi is based on the true story of an SLE patient. The novel tells the story of a little girl, Sarah, and her new friend, Farra, who has just moved into the neighbourhood. They soon become good friends. However, Farra develops a mysterious illness, which is finally diagnosed as Systemic Lupus Erythematosus (SLE). Sarah does not want to lose her friend and is always with Farra even when she is sick.
Through Pelangi, her diary, Sarah tells of her feelings and experiences as she sees Farra suffering from the illness. Because she cherishes their friendship, Sarah is willing to follow Farra β even if she has to move away from the neighbourhood, even if it means she will be away from her own family, as long as she is with her friend. Sarah truly admires Farra for her strength and perseverance in fighting the illness and to continue living. It is a story of hope for Lupus patients, especially children with Lupus.