Based off of minuiko's Blind Nico fan art.
The first thing to say was that he had always been blind. Most people assumed otherwise. There hadn't been an accident which resulted in his blindness. It's just the way that he was born.
Most people would assume that he had trouble going from one place to another but again that was not the case. At first it had been his sister, Bianca, who helped him get around. She would deal with the bullies and would help him in other areas where sight was needed. Like picking out clothes for himself, they were usually black.
Then a lawyer came and took them to a hotel. It was nice there or at least that's what Bianca said. He couldn't really tell. After awhile another lawyer came to get them and took them to a military school named Westover Hall. How they expected him to be able to do the things the others did he would never know?
Some people came along and told them they were children of the gods or maybe goddesses. He had always been shy and reserved. He would touch people's faces to 'see' what they looked like. They took him and Bianca to a place called Camp Half-Blood. But all he could help but feel was betrayed. Bianca left him on his own. In a strange new world.
When Bianca had gone off on the quest to save Artemis (and for Percy, Annabeth) he didn't feel alone. He still didn't feel alone. It felt like people were whispering directions in his ears but when he felt around no one was there.
Only three came back from the quest and his sister wasn't one of them. He felt like someone reached into his chest, pulled his heart out, and continuously crushed it. He ran because that is the only thing he could think of doing. The voices told him the way.
He discovered that the voices were actually ghosts and spirits. They helped him because his father was Hades, the god of the underworld. He learned how to depend on the voices as if they were his seeing eyes.
After many wars he still depended on them. Today for example.
"Excuse me. Can you tell me in which direction I could find a McDonalds?" He asked without hesitation.
"Go straight and you will reach the destination that you seek." He received in reply.
"You know. After all this time it is still creepy how much you sound like a GPS. Are you doing that one purpose?" All around him he could feel the cold presence of the dead, but he could feel their laughter.
"So this way then?" He asked while pointed in front of him.
"Yes." Answered a different ghost this time.
"Thank You." He said walking away in the directions of McDonalds. Not hearing the whispered exchange between the ghosts.
"He's grown up so much." One said to the other.
"And he is oh so polite. They sure don't make them like they used to." The other one replied.
"Come on we better catch up. We don't want him tripping over stuff." And that was the end of the conversation between the two ghosts as they hurried to go after the one they liked to call the Ghost King, Nico di Angelo.