Hmm, 'the second born book' is a tricky one without a specific title. In fantasy, sequel naming can get wild. Sometimes it's a numbered book, like 'The Two Towers' for the second Lord of the Rings volume. Other times, it's a subtitle, making it harder to pin down without the series name.
If we're talking about a series where the first book is about the 'firstborn' heir, then the second might follow a younger sibling navigating their shadow. That dynamic is everywhere, from political fantasies like 'The Traitor Baru Cormorant' (though that's a standalone) to family sagas in sci-fi. The core conflict usually involves inheritance, duty, and carving a unique path when you're not the chosen one.
Without the exact title, I'm just spinning theories. My guess is it centers on a second child's struggle for agency, often more complex than the firstborn's straightforward hero journey.