Wake Me Up Later
When you first meet Nico di Angelo, he probably isn't going to be smiling – unlike Percy or Leo – but that doesn't mean he doesn't smile at all. Just not all the time. But when he did, Nico felt a bit light-headed and he felt being lifted and his muscles moved upwards and lips curled. He smiled during training, finished showers, finished sparring. He enjoyed smiles.
Nico enjoyed smiles more when the people around him smiled. When the camp was singing and laughing at the camp fire, Nico smiled. It was a pleasant, happy feeling. He just didn't express it often.