Claim: Gag Manga Biyori is a 15-volume manga written by Kōsuke Masuda and serialized by Monthly Shōnen Jump and Jump Square from January 2000 – November 2014.
Evidence: 15 Good Day for Gag Manga) is a manga serialized in Monthly Shōnen Jump until July 2007 when the magazine ceased to publish. Kōsuke Masuda The manga continued serialization in its monthly successor, Jump Square. January 2000 – November 2014