How we cite our quotes: (Chapter.Paragraph)
Quote #4
He crouched with the neck of the dashiki pulled up over his head and screamed as the elevator shot up. It was a little scream, as screams go, but it felt like a blow to Arm. He had forgotten he was vulnerable to Eye's fear. (20.36)
We get to see the inner-workings of the relationship between the detectives here. Not only can Arm read people's minds, he also picks up on their emotions. Too bad for him that fear is one of those emotions. He becomes scared because Eye is, not because he has anything to fear himself.
Quote #5
The detectives ran as fast as they could. They slipped and slid on rocks and banged into trees. Only fear kept them ahead of the villagers. (26.1)
Even though fear is a bad thing a lot of the time, it can also be something positive. It's fear that puts a spring in the detectives' step, and they make a bolt for it simply because they are afraid of what will happen if they get caught. Let's hear it for fear (for once).
Quote #6
Sekai started screaming. Arm remembered too late how closely his mind was linked with hers. She must have seen the ground drop out from under his feet as the elevator shot up like a rocket. He tried to shift his thoughts, but Sekai's terror was too great. Her fear trapped him. (34.49)
Since Sekai and Arm's minds are linked, she gets upset when something bothers him. Of course stuff that adults deal with all the time is super scary for kids—that's why Arm has to distance himself from little Sekai. Notice how it's not something specific that scares Sekai, just regular old stuff that adults see and deal with day to day.