Who is Nico di Angelo ?

The son of Neptune

Nico meets Percy at Camp Jupiter , where he is visiting his half sister , Hazel Levesque . When they meet ,Nico is shocked but easily gains control. He poses as a so and ambassador of Pluto , and even though most of the campers see him as harmless , Hazel knows that Nico is more dangerous than Reyna , Octavian , and maybe even Jason Grace . Nico tells Percy about the return and defeat of Kronos ( referring to him as Saturn ), and about Gaia . Nico later tells Hazel , after Percy leaves with Frank Zhang , that he knows Percy , but Percy must regain his memories by himself , since he needs to find his own way at the camp and Nico can't interfere . It is later revealed that Nico was forbidden to do so by Hades himself , since the time wasn't right yet . Hazel and Nico had a time to talk when he mentioned about Bianca he's sister who died , he mentioned that he missed his sister and he wanted to see it .

Later Nico is shown to be observing the War Games from afar using a pair of binoculars . When Mars appears ,Mars glares at Nico while mentioning that people will no longer be held to death , implying that he knows about him saving Hazel's spirit . Nico is later shown in the meeting , where he is present as a Senator in a black toga , and the ambassador of Pluto. Nico supports Frank , Hazel and Percy by telling them about the first Gigantomachy , Alcyoneus , and Thanatos , all of which makes Reyna suspicious . However , Nico doesn't say anything Octavian protests and wins the argument . Nico leaves Camp Jupiter before Hazel to see if he could locate The doors of death from inside the Underworld .

During his search , Nico ( thinking he could go anywhere in the Underworld ) comes to close to Tatarus and gets pulled in by the dark gravity pit genetates ( similar to a black hole ) . He was presumably forced to drink liquid fire from the Phlegethon in order to survive . At some point during his horrifying journey through Tatarus , Nico encounters the goddess of misery Akhlys , who was impressed at how much sorrow and pain the son of Hades carried , claiming that there was little more that she could do for him . Though he fought back , Nico was eventually overwhelmed and defeated by the sheer number of Gaia's forces down in Tatarus .

Nico is later shown in one of Hazel's flashback blackouts . He finds Hazel in the Fields of Aphodel and brings her back to the mortal world to give her another chance at life.

During the quest for the god Thanatos , Gaia mentions that when she used Hazel , she was at least honest about it , unlike Nico who she claims was lying to Hazel . Gaia also says that Hazel should be happy that she captured him, and that he is now somewhere in Rome . Gaia later tells this to Percy and he promises that they will find out what happened to him .

When they free Thanatos , Hazel asks if Nico is alive. While Thanatos doesn't say if he is alive or dead , he does say they will find the answers in Rome . Later after Percy regains his memory , he calls Mrs. O ' Leary , much to Hazels surprise . He tells her that Nico could tell her the story before realizing what he had said . On the way back to camp Jupiter , Percy fully regains his memory, and is quite angry at Nico for not telling him about his past. After Polybotes is defeated , Hazel mentions that Pluto is tuming a blind eye to her to let her live and she feels that he wants her to find Nico .