An exchange diary (交換日記, kōkan nikki) is a notebook shared between friends, who take it in turns to write in their thoughts or other comments.
Exchange diaries were especially popular in Japan in the 1990s in elementary and junior high schools, particularly among girls.
More formal exchange diaries would be plain with the names of the participants written on the cover.
The format of an exchange diary can also be good for therapy, because it gives someone a platform to write about her problems and experiences.
Manga and anime series that involve exchange diaries: This Japanese literature–related article is a stub.