"You ready to go Lucy?" Natsu asked as he put out the fire.

 "Yeah. I've got everything packed up and good to go. Which way is the castle again?" Lucy said, not mentioning anything about what she heard Natsu say to himself.

 "West from here. Still about a day's worth away." Natsu said, following Lucy outside continued their journey.

 "Hey Natsu? I've always wondered something about your book." Lucy said after an hour of stressful silence between them.

 "And what would that be?" He asked, raising an eyebrow in question.

 "What would happen if I were to write in it? would it just be normal or-"

 Before Lucy could finish, Natsu had her pinned against a tree, making her drop the book, but it landing open.

 "Never, and I mean Never, write in the book. You understand?" Natsu said, making himself very clear. Lucy nodded in fear and fell to the ground as Natsu released her.

Natsu stepped away from her, as far as the books boundary allowed him to. He continued to take deep breaths as Lucy stared at him in shock and fear.

"W-what happens I-if I write in it?" She mumbled out quietly, not wanting him to get angered again. Natsu bit his tongue to calm down, then slowly turned to face her.

"You'll never write in it, so you don't need to know what happens. Don't even try to sneak in a scribnle, because I'll be able to sense it. Just pick up my book and let's get moving." Natsu said, calmer at this point, but regretting his actions towards Lucy.

 Lucy crawled over to the book and slammed it closed. She looked over at where Natsu once stood, and watched him disappear into the book's grasp.

First he talks to himself, then he rages out on me. What's he hiding?