Nico di Angelo
Nico is twelve years old in this book. His theory to gain an edge over the Titans is to make Percy invincible by having him bathe in the River Styx, similar to the myth of Achilles. It is shown that after Bianca died, Hades feels he has no competent child, repeatedly mentioning that Bianca could do a better job at fulfilling their father's demands than Nico. It is also revealed that the lawyer who removed the children from the Lotus Casino was Hades' lead Fury, Alecto, in disguise.