Rick Riordan said this quote
“ Images flashed through his mind. He saw Nico and his sister on a snowy mountain cliff in Maine, Percy Jackson protecting them from the manticore. Percy's sword gleamed in the dark. He'd been the first demigod Nico had ever seen in action. Later at Camp Half-Blood, Percy took Nico by the arm, promising to keep his sister Bianca safe. Nico believed him. Nico looked into his sea-green eyes and though, How can he possibly fail? This is a real hero. ”