Complex sentence: The single largest event featuring cosplay is the semi-annual doujinshi market, Comiket, held in Japan during summer and winter, attracting hundreds of thousands of manga and anime fans, where thousands of cosplayers congregate on the roof of the exhibition center.
Split into simpler sentences: The single largest event featuring cosplay is the semi-annual doujinshi market, Comiket, held in Japan during summer and winter. It attracts hundreds of thousands of manga and anime fans, where thousands of cosplayers congregate on the roof of the exhibition center.