icha icha (naruto)
Icha Icha (イチャイチャ, English TV: Make Out) is a series of adult novels written by Jiraiya after the commercial failure of The Tale of the Utterly Gutsy Shinobi. The Icha Icha novels are based on Jiraiya's experiences in love, particularly his rejections by Tsunade. When he's working on a new novel, he gathers "research" by peeping on women while they bathe. Teenagers are often curious about the books' contents, prompting their parents and other adults to go to great lengths to keep the books away from them.
Icha Icha is wildly popular, giving Jiraiya's checkbook a balance that is "filled with zeroes". Hatake Kakashi is a particular fan of the series; he enjoys reading the books even while in the middle of conversations.