At his core, Nico has a big heart, and an inquisitive personality. His sister was his world, and he and she had already been through a lot together by the time he meets Percy, but he doesn't come off as a damaged boy, protecting his heart. He's immediately curious about the demigods and excited to become a part of their lives. He's smart, nerdy, and pretty self-sufficient. He's also a fountain of questions. But that sweetness and innocence are short-lived.

Nico quickly becomes the character in the series who has probably been through the most, and it changes him profoundly. The loss of Bianca affects him deeply. From the point at which she dies, he begins to pull away, but he's unable to find acceptance from his father, and living in Hades, obsessively chasing Bianca's shade, brings him no happiness. Nico tries to be the lone wolf, the dark, brooding hero who doesn't need anyone. But in the end his heart won't allow it. He begins to put away his anger, and reach out again.

But while Nico starts to form friendships once more, he continues to maintain deep walls around himself. He cares about Hazel as a sister (though nothing can supercede Bianca), loves Percy, and grows to care for the rest of the Seven as friends and comrades. He would willingly sacrifice his life for them, and he doesn't want to see them suffer on any level. But at the same time, he believes that he can truly never be one of them, and that if they knew him, really knew him and who he was, that they would hate him. He's aware that most people find him creepy, just generally, and as a child of Hades, the outcast god, he simply doesn't fit in properly with the children of other Olympians. After spending 70 years in the Lotus Hotel, he is a child out of time. And even worse, he's gay, but grew up in the 1930s. On some level, he has internalized the values of that time, and he feels shame and self-loathing for his sexuality.

By the time I have chosen to draw Nico from, while he is kind and caring, he is quiet, brooding, and creepy. He often fades into the background, startling everyone when he suddenly puts some input into the conversation. He's very bright, and knowledgable about Greek and Roman myth. He has a knack for getting into places, including becoming an accepted part of Camp Jupiter and generally seen by the Romans as generally harmless, despite his creepy demeanor and status as a child of Pluto. He's incredibly self-sufficient and resourceful, surviving things that no other person has. But he hasn't come out of it unscathed. Though he is generally calm, if he feels threatened (for example, when Jason found out about his feelings for Percy), he can still react with anger, and will lash out to protect himself, like a cornered animal. He is scarred deeply by his experiences. His time in Tartarus nearly drove him insane.

But I think that's why he's drawn back to spending time with his friends, despite his self-loathing and his fears of rejection. He can't bring himself to isolate himself completely. He needs connection, needs love in his life. So he seeks his father's love, and failing that, he makes connections with a new sister - Hazel - and continues to follow Percy, protecting him when he can, and going to incredible measures to help him without any consideration for his own safety and sanity. He forms friendships with other demigods even though he believes they would hate him if they knew his heart. Because he can't stand to be alone.