firm belief in the character, strength, or truth of someone or something

Despite being upset at Bianca for leaving him, he wasn't going to sit around and let her go on a dangerous quest! He was amazed when learning about heroes' adventures, but letting your sister go on a quest which she could possibly not return from was a separate matter!

So he was going to sneak out and accompany her. Yes, he was new to this world. Yes, he lacked training. Yes, he probably wouldn't be much help. But Nico pushed all those thoughts out of the way, making sure she would be safe was enough of a reason to go. He was about to run after them when he heard,

"Wait."

Oh my god. Or oh my gods? Either way, Nico nearly jumped out of his skin. Who had followed him? He made sure to be stealthy, had he distracted himself?

A familiar face materialized next to him. How?!? Where had he come from?

It seemed like Nico wouldn't go. Percy had made it very clear that he, someone who had no experience and was too young for the trip, would face great dangers on this quest. But his sister. He had to protect her. Wait a second, he knew what to do.

"Maybe you're right. But, but you can go for me." Please go, protect her Percy.

After some convincing, it seemed like Percy would be going after them. After all, deep inside Nico knew Percy had originally planned on going to save Annabeth either way. He tried to ignore the sudden wave of jealousy that hit him.

"But you have to promise to keep my sister safe." He needed a confirmation, a hero like Percy is more than enough to look after his older sister.

"I...that's a big thing to promise, Nico, on a trip like this. Besides, she's got Zoë, Grover, and Thalia-" Nico's smile faltered.

"Promise,"

"I'll do my best. I promise that."

Nico released the tension in his body he didn't know he was holding. He could now breathe properly. His sister would be safe. Yeah, Percy would make sure nothing bad happens to her.

Because how can a hero fail?