Aside from the books which was about getting stronger type books, there wasn't really any book to pass time in both worlds. There were that kind of books, but they were mostly romantic books, and Leon wasn't into that. So hearing tales of sailors and occasionally listening their songs, calmed Leon's mind. Leon wasn't under stress, but after learning that somebody did something to his soul, he couldn't calm himself. When he killed the monsters to relieve his anger, it didn't solve it. It just calmed him a bit, but hearing tales and songs, Leon realized that he couldn't do anything about it at the moment, so he shouldn't be burdened by it, he should focus what he could do.