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.