* Protecting his friends: Throughout the book, Percy consistently puts the needs of his friends ahead of his own. He risks his life to save Annabeth from the Fury in the museum, and he goes to great lengths to protect Grover and the other half-bloods. He even sacrifices his own freedom to protect Luke, despite knowing that Luke is dangerous.
* Staying true to his word: Percy is a man of his word. He promises to find Zeus' lightning bolt and he sets out to do just that, even though it puts him in extreme danger. He doesn't give up, even when he's constantly being hunted.
* Defending the innocent: He shows loyalty to his mother by refusing to believe she was the thief, and he stands up to those who accuse her. He also feels a strong sense of loyalty to the other half-bloods, even those he doesn't know well, believing they deserve protection and a chance at a normal life.
* Loyalty to the gods: While he is initially hesitant about the Gods, Percy eventually comes to respect them, especially Poseidon, and is determined to prove himself worthy of his father's legacy.
* Loyalty to his cause: While he is initially skeptical of the quest, Percy eventually embraces his role as a hero and believes in his mission to find the lightning bolt and prevent a war between the gods.
These examples demonstrate that Percy is a deeply loyal character who puts the needs of others before his own. His loyalty is one of the reasons why he is such a compelling protagonist.