The origin story that appears to have the most evidence to support it actually blends from langaaaa's blog

Therefore, it is not surprising that the specific origins of anime and manga cosplay are highly debated topics among anime and manga otaku (Hlozek 2004). The origin story that appears to have the most evidence to support it actually blends the Japanese and North American contributions.Spiderman Costume
    In 1984 Takahashi Nobuyuki (known in the United States as "Nov Takahashi"), founder of and writer for Studio Hard, an anime publishing company, attended World-Con, a science fiction convention, in Los Angeles (Bruno 2002a; Hlozek 2004). CCosplay    Consequently, when he returned to Japan and wrote about his experiences at the convention, he focused on the costumed fans and the masquerade. Moreover, Takahashi encouraged his Japanese readers to incorporate costumes into their anime and manga conventions (Bruno 2002a).