Icha Icha (Earth-2356)

Icha Icha was a series of adult novels written by Jiraiya after the commercial failure of The Tale of the Utterly Gutsy Padawan. The Icha Icha novels were based on Jiraiya's experiences in love, particularly his rejections by Tsunade. When he worked on a new novel, he gathered "research" by peeping on women while they bathed. Icha Icha was wildly popular, giving Jiraiya's checkbook a balance that is "filled with zeroes". Obi-Wan Kenobi, Jiraiya's apprentice, was a particular fan of the series; he enjoyed reading the books even while in the middle of conversations.

Source

 * https://naruto.fandom.com/wiki/Icha_Icha