 At the end of The Son of Neptune, Nico travels through Tartarus to find the monstrous side of the Doors of Death, an experience which leaves him haunted and weak.In The Blood of Olympus, he nearly dies several times while "shadow-traveling", which involves melting into shadows and teleporting himself to different places.His sister whom he brought back from the dead, who goes by the name Hazel Levesque, is the daughter of Hades' Roman identity Pluto.