In "Obsidian" by Jennifer L. Armentrout, the protagonist navigates the complexities of her new life as she grapples with her feelings and the people around her. One significant character is her brother, who is described as moody, a trait that adds tension to their relationship. This moodiness hints at underlying issues, making their interactions both intriguing and challenging.

The book weaves themes of personal growth and the struggles of adolescence, as the narrator learns to cope with not just her brother's behavior but also her own insecurities. The dynamics of family, friendship, and self-discovery are explored throughout the narrative, making it relatable for many readers.