In The Lightning Thief, Percy feels extremely alone at first when he discovers his identity as a demi-god and is sent to his Poseidon's cabin at Camp Half-Blood all by himself. As the quest reveals itself, however, Percy is delighted to have Annabeth and Grover both volunteer to be his companions. Grover proves himself a loyal friend throughout Percy's adventures in the novel; as a keeper, he does his best to ensure Percy's safety, but he also acts as a friend and companion to Percy by counseling and encouraging him through difficult times. Like Grover, Annabeth also has to prove herself as a true friend to Percy, who is not completely sure of her motives at first. Annabeth refuses to quit the quest, and her practical nature like calling Percy "seaweed brain" help keep him grounded as well.
The helped him to settle into his identity as a demigod, and when Percy faces difficulties on his missions, such as when encountering Medusa, they assist him.