Nico, despite being very powerful, is extremely lonely, much like his father. He makes nearby people uncomfortable, partially due to his weapon of choice: a sword made of iron cooled in the Styx ("Stygian iron"), capable of absorbing monsters' essences rather than banishing them to Tartarus. Stygian iron, unlike celestial bronze and Imperial gold, can harm both mortals and immortals. In The Mark of Athena, he is captured by the giants Ephialtes and Otis to be used as bait. During The Blood of Olympus, Nico, with the help of Reyna Avila Ramirez-Arellano and Gleeson Hedge, transport the Athena Parthenos to Camp Half-Blood. Between The Blood of Olympus and The Hidden Oracle, he begins a relationship with Will Solace, a child of Apollo, after admitting to Percy that he had a crush on him. Nico’s suggestion that Percy takes on the curse of Achilles and his work to convince Hades to fight in The Last Olympian is crucial to the Olympians' success and earns him a short bout of fame. He is privy to the fact that there are two camps, one Greek and one Roman, before The Lost Hero, making him an important liaison between the two groups in the latter series. He brings his half-sister Hazel back from the dead and establishes her at Camp Jupiter. At the end of The Son of Neptune, Nico travels through Tartarus to find the monstrous side of the Doors of Death, an experience that 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, Hazel Levesque, whom he brought back from the dead, is the daughter of Hades' Roman identity Pluto. In The Hidden Oracle, Will Solace introduces him as his boyfriend to Apollo. Although their attraction for each other is hinted at in The Blood of Olympus, they are not seen getting together. After the three-legged death race, he is seen assisting Will to treat the injured patients. At the end of the book, he helps Apollo and the others fight after his and Will's canoe capsized. In The Tower of Nero, he and Will help to fight Nero and Nico is shown to have become depressed following the death of Jason Grace. At the end of the book, Nico is convinced that his friend the Titan Iapetus or 'Bob' is