Icha Icha

The series is the name of a series of adult novels authored by Jiraiya. Kakashi Hatake is a big fan of these books, and is seen reading one of them most of the time.

There are three books in the Ichas Icha series:

There's also an unofficial Icha Icha novel written by Naruto Uzumaki in the episode 177. Where Naruto finishes up Jiraiya's manuscript and sends it to the wrong place.
 * The first book to appear in the series. It was so famous that it was made into a movie. It is believed that Yukie from the first Naruto movie starred in this movie.
 * The second book. Also became a movie, as seen in episode 101.
 * The third book. Naruto Uzumaki gives this book to Kakashi when he returns to Konoha after a two-and-a-half year absence. Kakashi is later defeated by Naruto and Sakura Haruno, because they spoil the storyline of the book (but to only realize that Naruto made it up as Naruto didn't get past ten pages). In chapter 407 this book was revealed to be the key to helping to reveal Pain's true identity. When looking at the first words of pages 31, 8, 106, 7, 207, and 15, it showed the message, "The real one isn't with them."