Introduced in The Titan’s Curse, book three of the Percy Jackson series, Nico and Bianca di Angelo are at the Lotus ... let’s just say she doesn’t really appear much beyond the third book.

After planting that story seed in The Tower of Nero and conceiving a new book from Nico's perspective, Riordan decided he couldn't do it alone. In his first collaboration of this kind, Riordan ...

But most notably, book three introduces one of the series’ most popular and most groundbreaking characters: Nico di Angelo ... she doesn’t really appear after the third book).